Relationship between Sluggish cognitive tempo and Attention Deficit Hyperactivity Disorder in children: Current status and perspective

Introduction

ADHD is one of the most diagnosed disorders in children and adolescents, in children/adolescents clinics, whose global prevalence is ranging between 8 to 12%^(1–3). In Chile prevalence rates report 6.2% in students (Chilean Ministry of Health, 2008). Risk factors for children with ADHD for the disorder to linger on are unknown, although these have been linked with late treatment, severity of the condition and psychiatric comorbilities, such as personality disorders, among others ⁽⁵⁾⁽⁶⁾. ADHD causes negative/ adaptation consequences in children having such condition, in their families, at schools, in the society, on sanitary costs. These reasons, among others, support the research not only from the infant psychopathology, but also from the social/educational scenario. According to the DSM–5 (diagnosis/statistic Manual of mental disorders ) ADHD is a chronic neurobiological disorder, with evolving symptoms and probable genetic transmission, affecting between 5 to 10% of infant population, even reaching till adulthood in 60% of all cases ⁽⁷⁾.

 DSM–5 classifies ADHD in three subtypes: combined type (the child has two factors), with inattentive predominance (the child only meets the criteria for inattentive behavior) with hyperactive/impulsive predominance (the child only meets the criteria for hyperactivity/impulsivity conducts). Despite the efforts aimed to improve understanding, evaluation, diagnosis, and ADHD treatment, still there are some pending issues, being probably one of the biggest dilemmas⁽⁷⁾ that of diagnosis and evaluation.

 ADHD requires a clinical diagnosis. Still there are no objective tests valid enough for such purposes, so a diagnostic structure, based on the existence of two factors encompassing ADHD dimensions had to be used: i.e., inattentive behavior and hyperactivity/impulsivity conducts. During the last few years, various studies have been made on ADHD and coexistence of other pathologies. It has been described that a person with ADHD has six times more probability to suffer another psychiatric disorder than the rest of the population ⁽⁸⁾. 80% of all ADHD cases have comorbility with others disorders. According to this scenario, the problem would be to consider a possible attention disorder separated from combined ADHD, being a key aspect presence or absence of hyperactivity/impulsivity conducts ⁽⁹⁾.

 Despite inattention criteria are the same for combined ADHD than for Inattentive ADHD (the presence of higher or lower hyperactivity/impulsivity makes a difference in the diagnosis), currently many studies support the possible existence of a disorder, or at least a pure attentional dysfunction ⁽¹⁰⁾. The debate about the existence of a pure attentional dysfunction has created opposite points of view. On the one hand there are those who believe that inattentive behavior in ADHD may be a disorder different from SCT; on the other hand, there are those who believe if there is a pure inattention/concentration disorder, probably it is made up of various conducts, although related with those of ADHD inattention. From this point of view, various investigations support SCT presence to talk about a very concrete type of child: slow thinking and slow motor behavior, normal intelligence and conduct, with an excessively fluctuating level of concentration, unfocused and sunk into a dreamy state ^(11–14).

In this sense, even though comorbility among disorders is usual, there is a high relationship between SCT and ADHD, specifically with the inattentive subtype of such disorder (ADHD–IN). Estimations consider that between 30 to 59% of patients diagnosed with ADHD–IN have SCT symptoms; therefore, SCT could affect cognitive/executive functions in children^(15–19). During the last few years an increasing interest on the evaluation/detection modes of SCT symptoms has arisen. Before the emerging testing in non clinical fields, i.e. formal educational areas, what is the actual SCT/TADH relationship is still to determined, and what are the social problems arising from this. It is also necessary to know if if this is a disorder that predicts anxiety and depression or it is simply related with the latter.

Methodology

In March 2019 a systematic literature search was made in the data base of Web of Science, PubMed Scopus, both in English and Spanish, about reports published till 2019, and relevant information on SCT/ADHD, using the following search engines with Boolean operators “AND – OR”: “sluggish cognitive tempo”, “attention deficit”, “hyperactivity disorder”, “clinical trials”, “epidemiological cognitive and executive functions. During the works search, studies on a single case, other systematic reviews or works not presenting an experimental design were excluded. The information of the chosen works was transferred into a Microsoft Word document, where the following information was gathered: title, authors, year of publication, objectives, size of the sample and findings between SCT and ADHD (Figure 1).

Figure 1. Phases of systematic review

Results

Conceptualization of Sluggish Cognitive Tempo

The study of the SCT, as a construct was found in most ADHD disorders investigations. Given the clear association between SCT and ADHD, a constant/increasing interest to find out whether SCT is a construct empirically different, with its own dimensions and differentiated from ADHD or not, and also to learn about its operation and psychosocial impact ⁽²⁰⁾. There are various opinions about the definition of SCT dimensions, its functions, its description of clinical usefulness, although, most research has been focused on SCT review and its evolution^(21–23). Among the most usual features present in this group of subjects are: slow execution of tasks, forgetful, drowsy, daydreaming, absent minded, unmotivated, usually living in another world, confused, having a low performance in some neuropsychological test, low scores when measuring executive functions, reduced alertness, irregular orientation ⁽²⁴⁾.

Because of all the foregoing, SCT is associated to the inattention factor of ADHD, with a lack of hyperactivity and impulsivity⁽¹⁷⁾. The research has been rather focused on SCT as a group of symptoms different from ADHD⁽²⁰⁾. Authors, such as Barkley et al.⁽⁹⁾ argue that SCT may be a psychiatric disorder on its own, separated from ADHD, with a prevalence rate –estimated among young people– of 5 – 6%. Despite there are various investigations focused on attention difficulties and on ADHD, few investigation works –during the last years– have been focused on SCT, although results are encouraging, it is necessary to move forward on symptomatological aspects, such as: comorbility, evolution, neural correlate, associated risks.
On the other hand, despite the importance of the research and the findings, there is still a need to agree on criteria to recognize and validate SCT, highlighting differences between SCT and TDAH9. Several studies have reported that TLC dimension is different from the inattention symptoms ⁽²⁵⁾.

Symptomatology for Sluggish Cognitive Tempo

One of the main problems found when studying TLC dimension is the lack of reliability and validity of the construct. The most significant finding has been obtained by using the confirmatory factor analysis, accepting a three–factor model which allows to differentiate inattention symptoms, hyperactivity–impulsivity, and SCT. Besides, high correlations between ADHD and those of inattention were found; however, these are moderate when compared with hyperactivity–impulsivity, assuming the existence of SCT construct associated to inattention described in DSM–4 for ADHD^{(26) (27)}. On the other hand, SCT symptoms were confirmed to be a factor different from the dimensions of inattention symptoms and hyperactivity of ADHD, thus emerging SCT as a separate construct ^(28–30). Regarding validity of the construct, a study by Lee et al.⁽³¹⁾ states the existence of 8 conducts describing SCT symptoms, showing an adequate convergent/discriminate validity. Therefore, even though the statistic validity of the construct seems to be proved, its clinical diagnostic and usefulness still has not been proved⁽¹⁴⁾.

This distinctive feature of SCT and ADHD symptoms, is also stated in direct observation studies of children during the tests execution in a school environment⁽³²⁾, as well as in USA population14 in a wide sampling of college students⁽²²⁾. On the other hand, SCT symptoms identify a group of children/adolescents, even within samples with inattentive ADHD ^(33)(34); however, results in this type of research have not been so strong or numerous, as when SCT groups are selected from regular population or other specific samples for SCT⁽³⁵⁾.

Neuropsychological characteristics on Sluggish Cognitive Tempo Dimension

Some studies have confirmed differences in neuropsychological profiles of ADHD subtypes although there is controversy in the results obtained⁽²⁾. Some have determined a specific deficit in the executive function⁽⁵⁰⁾. Currently, the association between TLC and neuropsychological functions still remain under studied51. Hinshaw et al.⁽⁵¹⁾ state that girls with ADHD and high levels of SCT have a low speed in two motor neuropsychological tasks . Some authors have reported academic hindrances –in general– in children and adults with SCT^(52–54).

Bauermeister et al.⁽²⁵⁾ do not objectify links between SCT and processing speed. These findings are not consistent with the hypothesis that children with SCT have a lower motor/processing speed ⁽²⁴⁾. We may infer that in most studies subjects with ADHD have a worse executive function than subjects with SCT symptoms; and these are usually featured by difficulties regarding: sustained attention⁽⁵⁵⁾ selective attention⁽⁵⁶⁾, variability in spatial memory⁽¹⁹⁾, arousal difficulties ⁽⁵⁷⁾, in their working memory⁽²³⁾, when decoding information from social signals⁽⁵⁸⁾, in lower motor/ processing speed^(24)(51)(56), in mathematical skills, organization difficulties and problems resolution⁽⁵⁹⁾. Huang–Pollock et al.⁽⁵⁶⁾ state that children with ADHD and with high levels of SCT had dysfunctional early selective attention, typical of ADHD. Regarding sustained attention, authors do not agree, as some report worse sustained attention in children ADHD with high levels of SCT; others report that ADHD with high levels of SCT have fewer problems in sustained attention⁽⁵⁹⁾.

However, other investigations suggest that SCT is not a executive function disorder, just as experienced in every day activities, and in most questionnaires on executive function appraised during these studies⁽⁶⁰⁾. These findings could support the idea that SCT involves alteration of some type of attention, which is not the same attention altered in ADHD. Regarding working memory in community samples of SCT⁽⁶¹⁾ it was reported that this could be a factor to be taken into account when evaluating children. Some spatial memory–related reports state higher variability in those subjects with higher levels of SCT⁽¹⁹⁾. This situation does not happen neither with reaction time nor with the verbal memory.
On its part Wahlstedt & Bohlin⁽⁵⁵⁾ report that inattention described in DSM–IV was exclusively related with inhibitory control and working memory, nut this situation is not replicable for the SCT. Regarding processing speed (PS), there are some contradictory studies, as well; some of them report a deficit in PS in children with high SCT ^(16)(21)(24), while others do not appreciate such correlation ⁽²⁵⁾. These contradictions may arise because of the use of various measuring instruments, lack of control of the variables in some of the studies, or maybe because the samples were made with children suffering ADHD, which could influence on results.

Impact of the Sluggish Cognitive Tempo dimension in children´s life

TLC dimension, regardless if it is a a disorder or not, impacts on various areas of children´s lives; however, results are just a few, varied and sometimes contradictory. Research reveals that SCT is mainly associated with social problems ^(14)(15)(18) even after controlling overlapping with ADHD. The nature of social problems related with SCT, according to Mikami et al.⁽⁵⁸⁾ differs from those manifested in ADHD (aggressiveness, emotional disturbance, disruptive conduct). These are more related with the presence of social withdrawal and isolation⁽⁶²⁾. These results are consistent with other previous studies, after controlling demographic factors and comorbility. Among these and other reasons, for which SCT is associated with social withdrawal, and social anxiety, whether if it was studied independent from ADHD, or within the groups with this disorder. However, it is necessary to find the cause of this relationship. Some hypothesis state that maybe SCT symptom of daydreaming leads to social difficulties which may increase anxiety or depressive symptomatology.

Another option could be that people having high levels of SCT are more keen to show anxiety/depression symptoms, linked in turn to social problems. OR may be the cause is totally opposite: more symptoms of anxiety/depression cause social withdrawal or SCT symptomatology. This last hypothesis is not quite possible, as while it is true that SCT is related with anxiety and depression, correlations are moderate and share only a minimum variance^(14)(15)(18).

Saxbe & Barkley⁽²²⁾ reported that few children with SCT had had previous diagnosis of depression, despite this percentage was significantly high compared with ADHD groups and with the control group. Likewise some previous investigations match ^(26)(27), where SCT is more linked with depression rather than with anxiety, by controlling parents´ anxiety and depressive symptoms⁽²⁰⁾. Another one of the remarkable aspects when studying SCT, is focused on academic difficulties, although there is some controversy among authors, as many times no direct reports are available (from parents and teachers), or else because most students with SCT go unnoticed in their class. However, more academic difficulties have been reported on people with high levels of SCT ^(52)(53)(54); however, there are other studies not supporting such relationship⁽³⁵⁾. This controversy may arise, because many studies take into account SCT symptomatology in groups of children with ADHD, segregated according to high/low scores in such construct⁽⁶³⁾.

Sluggish Cognitive Tempo and its relationship with academic performance in children

The relationship between SCT and academic performance has caused high interest and many discussions. Langberg et al.⁽⁷³⁾ studied the association between SCT and academic performance in 52 adolescents with ADHD and reported different results. The authors proved the Slowness SCT Subscale, according to parents predicts disruptions in academic performance, i.e. deficit in organization skills and problems to perform duties, beyond ADH symptoms and other characteristics associated with the academic world. By contrast, the Sub–scale Low initiative/Persistence of SCT, according to the teachers, predicted difficulties when performing duties and it was the only SCT variable that predicted medium school marks beyond ADH symptoms and other covariables. These results have not been fully guaranteed, as McBurnett et al.⁽⁶¹⁾ did not find a relationship between the Low–initiative Factor and academic performance.

However, total score in SCT and its Drowsy/Tired Factor are inversely associated with academic performance, even after controlling influence of ADHD. On its part, Becker et al.⁽²⁰⁾ analyzed the relationship of SCT with academic performance difficulties in a sample of 72 college students with ADHD diagnosis evaluated with the Barkley´s BAARS–IV Scale made up of four factors: SCT, IN, HI and Impulsivity. Controlling the effect of the other factors, SCT was relevantly correlated with academic performance problems (apart from measures of anxiety and depression). From a more clinical point of view, Marshall et al.⁽³⁴⁾ identified three groups of young subjects diagnosed with ADHD: ADHD–C, ADHD–IN with high SCT and ADHD–IN with low SCT and analyzed their differences regarding academic performance. SCT levels were measured with the three items used in the DSM–IV trials. The results proved that both groups with ADHD–IN had more difficulties in performance in the classroom, compared with the group ADHD–C. Even more, the group ADHD–IN with high SCT was the only one that had problems when performing duties, even when disorders of disruptive behavior were absent.
According to Barkley^(74–76), low academic performance and school failure are common among hyperactive children and are one of parents´ most frequent concerns. Academic performance usually is a consequence of impulsivity, attention problems, other associated psychopathological components, quality of environmental reinforcements and the capacity to develop relieving gears.

It is likely enough that, due to attentional/memory/executive control difficulties, children have a poor school performance, with low marks, and a higher percentage of cases requiring to receive special education support. Numerous investigations have inquired about the relationship between infant executive function and academic performance of the latter in mathematics^(77–79), reading, and problems solving ⁽⁸⁰⁾. Currently there is some agreement among various authors, regarding a relationship between executive performance and academic performance. For instance, Geary et al.⁽⁸¹⁾ performed a study aimed to evaluate the relationship between children´s performance in mathematics tests and their performance in tasks related with working memory and processing speed. Geary et al.⁽⁸¹⁾ reported that children with a normal performance were faster and more accurate when performing tasks related with identifying numeric arrays, recovery and retention of numeric information, lineal estimation and counting capacity.

Understanding that SCT could be a pure attention disorder, we should wonder what role parents, teachers and all education agents have in detecting and early intervening such symptoms, or else, how schools could be prepared to offer timely and personalized responses before each demand. A study made by Barkley⁽¹⁴⁾ reports that SCT predicts academic problems and concretely contributes to the problems on written language, reading, organization skills and execution of school tasks. This same pattern is evident in other recent studies with school children^(60)(62) alluding difficulties in mathematical performance, and become more evident in SCT rather than in ADHD ^(60)(62)

Discussion

 One of the difficulties involved in SCT is the lack of questionnaires and measuring instruments useful and specific of the construct, and also the lack of coherence when choosing the items in the various studies. In this line, Penny et al.⁽¹⁸⁾ developed an SCT scale for parents and teachers, first identifying 26 behaviors associateQd to SCT construct. Later, with the help of clinical experts they identified the most representative behaviors, and the Scale was reduced to 14 items. After the screening, high correlations between SCT and ADHD–IN were found, lower correlations with ADHD hyperactive/impulsive subtype (ADHD–HI), Oppositional Defiant Disorder (ODD). When controlling the influence between SCT and TDHA–IN, high levels of SCT were found to be associated with low levels of ADHD–HI and TND.

Barkley(14) performed a study with 1,922 children adolescents, and proved that SCT and ADHD are different symptomatological dimensions, therefore defining different disorders and highly related, thus proving good validity of the construct. Table # 2 shows some studies on reliability and validity of Sluggish Cognitive Tempo in samples with children and adolescents. Despite significant progress, we still do not know what factors make up SCT, or if these factors are universal. That is to say, just as it happens with factors, such as ADHD inattention and hyperactivity/impulsivity, SCT factors may appear in school population of various countries and cultures. Pfiffner et al.⁽⁸²⁾ developed a behavior strategies program for parents and teachers, focused on symptoms and academic problems of children with high SCT symptomatology. Successful results are an example to keep studying potential specific therapies for SCT.

Table # 1. Some investigations performed in Sluggish Cognitive Tempo and attention deficit disorder with hyperactivity during the last few years.

CBCL = Child Behavior Checklist; DSM = Diagnostic and Statistical Manual for Mental Disorders; DOF = Direct Observation form; ECRS = Emory Combined Rating Scale; SCT = Sluggish Cognitive Tempo; H/ I = Hyperactivity/Impulsivity; I = Inattention; H = Hyperactivity; SCT = Sluggish Cognitive Tempo; ADHD–I = Disorder due to Attention Deficit with Hyperactivity subtype Inattentive; ADHD–C = Disorder due to Attention Deficit With Hyperactivity Subtype Combined; SCT = Sluggish Cognitive Tempo; TRF = Teacher Report Form

From a psychological point of view, assuming that SCT may be different from ADHD, we cannot assume that behavioral/cognitive therapy or training on social skills are effective for SCT. However, in the light of the close relationship of SCT with internalized disorders, could be expectable that behavioral/cognitive therapy or training on social skills works for handling social/cognitive problems of SCT.

Despite the efforts to improve understanding, evaluation, and diagnosis treatment of ADHD, still there are some pending issues, and one of the biggest dilemmas are probably diagnostic and evaluation. We still do not have objective tests valid enough for such purposes, appealing to a diagnostic structure based on two factors representing ADHD dimension: inattentive behavior and hyperactivity/impulsivity conducts. The problem lies when considering a possible attention disorder, separated from Combined ADHD. The presence or absence of hyperactivity/impulsivity conducts is a key aspect. Despite inattention criteria are the same for Combined ADHD than for Inattentive ADHD, currently many studies support the possible existence of a disorder, or at least of a pure attentional dysfunction. The debate about the existence of a pure attentional dysfunction has generated opposed approaches: on the one hand are those who believe that inattentive behavior in ADHD may be a different disorder; on the other hand, are those who state that if there is an attention disorder or pure concentration disorder, probably it is made up of various conducts, that even if they are related with ADHD inattention, they may represent an independent dimension.

Table # 2. Reliability/validity of the Sluggish Cognitive Tempo en samples of children adolescents.

CADBI = Child And Adolescent Disruptive Behavior Inventory; CBCL = Child Behavior Checklist; CCI = The Child Concentration Inventory; ECRS = Emory Combined Rating Scale; PC = Population Clinical; PG = Population General; SCT = Sluggish Cognitive Tempo; LD =Learning Disorder; SCT= Sluggish Cognitive Tempo; TRF = Teacher Report Form

References

1. American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders. 4 ed. TR. Washington DC: APA.
   
2. Camprodon E, Duñó L, Batlle S, Estrada X, Aceña M, Marrón M, Torrubia R, Pujals E, Martín LM, Ribas-Fitó N. El Tempo Cognitivo Lento: revisión de un constructo. Revista de Psicopatología y Psicología Clínica. 2013;18:151-168
   
3. Giménez-García L. Tratamiento cognitivo conductual de problemas de conducta en un caso de trastorno por déficit de atención con hiperactividad. Revista de Psicología Clínica con Niños y Adolescentes. 2014;1:79-88
   
4. Thomas R, Sanders S, Doust J, Beller E, Glasziou P. Prevalence of Attention-Deficit/Hyperactivity Disorder: A Systematic Review and Meta-analysis. PEDIATRICS. 2015;135:1-8
   
5. Kessler RC, Adler LA, Barkley R, Biederman J, Conners CK, Faraone SV, Greenhill, LL. Patterns and predictors of attention deficit/hyperactivity disorder persistence into adulthood: results from the national comorbidity survey replication. Biol Psychiatry. 2005;57:1442-51.
   
6. Vegue-González M, Álvaro-Brun E, Santiago-Sáez A, Kanaan-Kanaan A. Retrospective evaluation of attention deficit hyperactivity disorder with the Wender Utah Rating Scale in a sample of Spanish prison inmates. Journal of Forensic Sciences 2011;56:1556-1561
   
7. American Psychiatric Association. Manual Diagnóstico y Estadístico de los Trastornos Mentales (DSM-IV-TR), 1ª Ed. Barcelona: Editoral MASSON. 2002.
   
8. Brown, T. E. Trastorno Por Déficit De Atención: Una Mente Desenfocadaen Niños Y Adultos. Barcelona: Masson (2006).
   
9. Barkley RA. Sluggish Cognitive Tempo (Concentration Deficit Disorder?): Current Status, Future Directions, and a Plea to Change the Name. Journal of Abnormal Child Psychology. 2014;42:117-125
   
10. Mueller AK Tucha L, Koerts J, Groen Y, Lange KW, Tucha O. Sluggish cognitive tempo and its neurocognitive, social and emotive correlates: a systematic review of the current literature. J Mol Psychiatry. 2014;2:5
    
11. Lahey BB, Pelham WE, Schaughency EA, Atkins MS, Murphy HA, Hynd GW, Russo M, Hartdagn S, Lorys-Vermon A. Dimensions and types of attention deficit hyperactivity disorder. Journal of the American of Child and Adolescent Psychiatry 1988;27:330-335
    
12. Barkley RA, Grodzinsky G, DuPaul G. Frontal lobe functions in attention deficit disorder with and without hyperactivity: a review and research report. Journal of Abnormal Child and Psychology. 1992;20:163-88
    
13. Barkley, R.A. Distinguishing sluggish cognitive tempo from attention defi cit/hyperactivity disorder in adults. Journal of Abnormal Child and Psychology. (2011). doi.org/10.1037/a0023961
    
14. Barkley RA. Distinguishing sluggish cognitive tempo from attention deficit hyperactivity disorder in adults. Journal of Abnormal Psychology. 2012;121:978-990
    
15. Carlson CL, Mann M. Sluggish cognitive tempo predicts a different pattern of impairment in the attention deficit hyperactivity disorder, predominantly inattentive type. Journal of Clinical Child and Adolescent Psychology. 2002;31:123-129.
    
16. Garner AA, Marceaux JC, Mrug S, Patterson C, Hodgens B. Dimensions and correlates of attention deficit/hyperactivity disorder and sluggish cognitive tempo. Journal of Abnormal Child Psychology. 2010;38:1097-1107
    
17. McBurnett K, Pfiffner LJ, Frick PJ. Symptom properties as a function of ADHD type: an argument for continued study of sluggish cognitive tempo. Journal of Abnormal Child Psychology. 2001;29:207-13
    
18. Penny AM, Waschbusch DA, Klein RM, Corkum P, Eskes G. Developing a measure of sluggish cognitive tempo for children: content validity, factor structure, and reliability. Psychological Assessment. 2009;21:380-389
    
19. Skirbekk B, Hansen BH, Oerbeck B, Kristensen H. The relationship between sluggish cognitive tempo, subtypes of attention-deficit/hyperactivity disorder, and anxiety disorders. Journal of Abnormal Child Psychology. 2011;39:513-25
    
20. Becker SP, Langberg JM, Luebbe AM, Dvorsky MR, Flannery AJ. Sluggish cognitive tempo is associated with academic functioning and internalizing symptoms in college students with and without attention-deficit/hyperactivity disorder. Journal of Clinical Psychology. 2014;70:388-403
    
21. Adams ZW, Milich R, Fillmore MT. A case for the return of attention-deficit disorder in DSM- 5. The ADHD Report. 2010;18:1-6.
    
22. Saxbe C, Barkley RA. The other attention disorder? Sluggish cognitive tempo vs. ADHD: update for clinicians. J Psychiatr Pract. 2014;20:38-49.
    
23. Diamond A. Attention-deficit disorder (attention-deficit/hyperactivity disorder without hyperactivity): A neurobiologically and behaviorally distinct disorder from attention deficit/hyperactivity disorder (with hyperactivity). Development and Psychopathology. 2005;17:807-825.
    
24. Milich R, Ballentine AC, Lynam DR. ADHD/combined type and ADHD/predominantly inattentive type are distinct and unrelated disorders. Clinical Psychology: Science and Practice. 2001;8:463-488.
    
25. Bauermeister JJ, Barkley RR. Bauermeister JA, Martínez JV, McBurnett K. Validity of the Sluggish Cognitive Tempo, Inattention and Hyperactivity Symptom Dimensions: Neuropsychological and Psychosocial Correlates. Journal of Abnormal Child and Psychology. 2012;40:683-697.
    
26. Hartman CA, Willcutt EG, Rhee SH, Penington BF. The relation between sluggish cognitive tempo and DSM–IV ADHD. Journal of Abnormal Child Psychology. 2004;3: 491-503.
    
27. Jacobson LA, Murphy-Bowman SC, Pritchard AE, Tart-Zelvin A, Zabel TA, Mahone, EM. Factor structure of a sluggish cognitive tempo scale in clinically referred children. Journal of Abnormal Child Psychology. 2012;40:1327-1337.
    
28. Becker SP, Langberg JM. Sluggish cognitive tempo among young adolescents with adhd: relations to mental health, academic, and social functioning. Journal of Attention Disorders. 2013;17:681-689
    
29. Lee S, Burns L, Snell J. Validity of the sluggish cognitive tempo symptom dimension in children: sluggish cognitive tempo and ADHD-Inatention as distinct symptoms dimensions. Journal of Abnormal Child Psychology. 2013.
    
30. Willcutt EG, Chhabildas N, Kinnear M, DeFries JC, Olson RK, Leopold DR, Keenan JM, Pennington BF. The internal and external validity of sluggish cognitive tempo and its relation with DSM-IV ADHD. Journal of Abnormal Child Psychology. 2013;42:21-35
    
31. Lee S, Burns GL, Snell J, McBurnett K. Validity of the sluggish cognitive tempo symptom dimension in children: Sluggish cognitive tempo and ADHD-Inattention as distinct symptom dimensions. Journal of Abnormal Child Psychology. 2014;.42:7-19.
    
32. McConaughy SH, Ivanova M, Antshel K, Eiraldi RB. Standardized observational assessment of Attention Deficit/ Hyperactivity Disorder Combined and Predominantly Inattentive Subtypes: I. Test session observations. School Psychology Review. 2009a;38:45-66.
    
33. Capdevila-Brophy C, Artigas-Pallares J, Navarro-Pastor JB, García-Nonell K, Rigau-Ratera E, Obiols JE. ADHD predominantly inattentive subtype with high sluggish cognitive tempo: a new clinical entity? Journal of Attention Disorders. 2012;18:607-16.
    
34. Marshall SA, Evans SW, Eiraldi RB, Becker SP, Power TJ. Social and academic impairment in youth with ADHD, predominantly inattentive type and sluggish cognitive tempo. Journal of Abnormal Child Psychology. 2014;42:77-90.
    
35. Belmar M, Servera M, Becker SP, Burns GL. Validity of Sluggish Cognitive Tempo in South America: An Initial Examination Using Mother and Teacher Ratings of Chilean Children. Journal of Attention Disorders. 2015;1-6.
    
36. Trujillo-Orrego N, Pineda DA, Uribe LH. Validez del diagnóstico de trastorno por déficit de atención/hiperactividad: de lo fenomenológico a lo neurobiológico (I). Rev Neurol. 2012;54:289-302
    
37. Stefanatos GA, Baron I.S. Attention-deficit/hyperactivity disorder: A neuropsychological perspective towards DSM-V. Neuropsychology Review. 2007;17:5-38
    
38. Sandín, B. DSM-5: ¿Cambio de paradigma en la clasificación de los trastornos mentales? Revista de Psicopatología y Psicología Clínica. 2013;18:255-286
    
39. Echeburúa, E., Salaberría, K., Cruz-Sáez, M. Aportaciones y Limitaciones del DSM-5 desde la Psicología Clínica. Terapia psicológica 2014;32:65-74
    
40. American Psychiatric Association Diagnostic and statistical manual of mental disorders (DSM-5), Washington, D.C.: American Psychiatric Association 2013.
    
41. Lepe-Martínez N, Pérez-Salas C, Rojas-Barahona CA, Ramos-Galarza C. Executive Functions In Preschool Children With And Without Language Disorders. Revista Ecuatoriana de Neurología. 2017;26:197-202
    
42. Verdejo-García A, Bechara A. Neuropsychology of Executive Functions. Psicothema. 2010;22:227-235.
    
43. Carlson SM, Moses LJ. Individual differences in inhibitory control and children's theory of mind. Child Development. 2001;72:1032-1053.
    
44. McClelland MM, Cameron CE, Connor C, Farris CL, Jewkes AM, Morrison FJ. Links between behavioral regulation and preschoolers’ literacy, vocabulary, and math skills. Developmental Psychology. 2007;43:947-959.
    
45. Tropper B, Marton K, Russo-Victorino K, Shafer V, Schwartz R. Research on Executive Functions in Children with SLI. Comunicación presentada en la convención anual de The American Speech-Language-Hearing Association, el 21 de noviembre de 2008.
    
46. Meltzer L. Executive Function and Education. From theory to practice. New York, NY: The Guilford Press. 2007.
    
47. Meltzer L. Promoting executive function in the classroom. New York, NY: The Guilford Press. 2010.
    
48. Baddeley A. Working memory, thought, and action. Oxford: Oxford University Press 2007.
    
49. Posner MI. Cognitive neuroscience of attention. New York: Guilford Press. 2011.
    
50. Nigg JT, Blaskey L, Huang-Pollock C, Rappley MD. Neuropsychological executive functions and ADHD DSM-IV subtypes. Journal of the American Academy of Child and Adolescent Psychiatry. 2002;41:59-66.
    
51. Hinshaw SP, Carte ET, Sami N, Treuting JJ, Zupan BA. Preadolescent girls with attention-deficit/hyperactive disorder II: Neuropsychological performance in relation to subtypes and individual classification. Journal of consulting and Clinical Psychology. 2002;70:1099-1111.
    
52. Frazier TW, Youngstrom EA, Glutting JJ, Watkins MW. ADHD and achievement: Metaanalysis of the child, adolescent, and adult literatures and a concomitant study with college students. Journal of Learning Disabilities. 2007;40:49-65.
    
53. Friedman-Weieneth JL, Harvey EA, Youngwirth SD, Goldstein LH. The relation between 3-year old children’s skills and their hyperactivity, inattention, and aggression. Journal of Educational Psychology. 2007;99:671-681.
    
54. Massetti GM, Lahey BB, Pelham WE, Loney J, Ehrhardt A, Lee SS, Kipp H. Academic achievement over 8 years among children who met modified criteria for attention-deficit/ hyperactivity disorder at 4-6 years of age. Journal of Abnormal Child Psychology. 2008; 36:399-410.
    
55. Wåhlstedt C, Bohlin, G. DSM-IV defined inattention and sluggish cognitive tempo: Independent and interactive relations to neuropsychological factors and comorbidity. Childdren Neuropsychology. 2010;16:250-365
    
56. Huang-Pollock CL, Nigg JT, Carr TH. Deficient attention is hard to find: Applying the perceptual load model of selective attention to attention deficit hyperactivity disorder subtypes. Journal of child psychology and psychiatry. 2005;46:1211-1218.
    
57. Barkley RA, DuPaul GJ, McMurray MB. Comprehensive evaluation of attention deficit disorder with and without hyperactivity as defined by research criteria. Journal of Consulting and Clinical Psychology. 1990;58:775-789.
    
58. Mikami AY, Huang-Pollock CL, Pfiffner LJ, McBurnett K, Hangai D. Social skills differences among attention deficit/ hyperactivity disorder types in a chat room assessment task. Journal of Abnormal Child Psychology. 2007;35:509-521.
    
59. Capdevila-Brophy, C., Artigas-Pallarés, J., & Obiols-Llandrich, J. E. Tempo cognitivo lento: ¿síntomas del trastorno de déficit de atención/hiperactividad predominantemente desantento o nueva entidad clínica? Sluggish cognitive tempo: symptoms of Attention deficit/hyperactivity disorder predominantly inattentive subtype or a new clinical entity? Revista de Neurología. 2006:42:127-134
    
60. Willcutt EG, Chhabildas N, Kinnear M, DeFries JC, Olson RK, Leopold DR, Keenan JM, Pennington BF. The internal and external validity of sluggish cognitive tempo and its relation with DSM-IV ADHD. Journal of Abnormal Child Psychology. 2013;42:21-35
    
61. McBurnett K, Villodas M, Burns GL, Hinshaw SP, Beaulieu A, Pfiffner LJ. Structure and validity of sluggish cognitive tempo using an expanded item pool in children with attention-deficit/ hyperactivity disorder. Journal of Abnormal Child Psychology. 2014;42: 37-48
    
62. Marshall, S.A., Evans, S.W., Eiraldi, R.B., Becker, S.P., & Power, T.J. Social and academic impairment in youth with ADHD, predominantly inattentive type and sluggish cognitive tempo. Journal of Abnormal Child Psychology. 2014;42:77-90.
    
63. Watabe Y, Owens JS, Evans SW, Brandt NE. The relationship between sluggish cognitive tempo and impairment in children with and without ADHD. Journal of Abnormal Child Psychology. 2013;42:105-15.
    
64. Stright, A.D., Gallagher, K.C. & Kelley, K. Infant temperament moderates relations between maternal parenting in early childhood and children's adjustment in first grade. Child Dev. 2008;79:186-200.
    
65. Rudasill KM, Gallagher KC, White JM. Temperamental attention and activity, classroom emotional support, and academic achievement in third grade. J Sch Psychol. 2010;48:113-34.
    
66. Lee Y, Sugai G, Horner RH. Using an instructional intervention to reduce problem and off-task behaviors. Journal of Positive Behavior Interventions. 1999;1:195-204.
    
67. Tuckman, B.W. The effect of learning and motivation strategies training on collage students archievement. Journal of collage Student Development. 2003;44:430-437.
    
68. Lassen SR, Steele MM, Sailor W. The relationship of school-wide positive behavior support to academic achievement in an urban middle school. Psychology in the Schools. 2006;43:701-712.
    
69. Westerlund M, Lagerberg D. Expressive vocabulary in 18-month-old children in relation to demographic factors, mother and child characteristics, communication style and shared reading. Child Care Health Dev. 2008;34:257-66.
    
70. Blondal KS, Adalbjarnardottir S. Parenting practices and school dropout: a longitudinal study. Adolescence. 2009;44:729-49
    
71. Bohanon H, Fenning P, Carney K, Minnis M, Anderson-Harris S, Moroz K, et al School-wide application of urban high school positive behavior support: A case study. Journal of Positive Behavior Interventions. 2006;8:131-145.
    
72. Algozzine B, Algozzine KM. Facilitating academic achievement through school wide positive behavior support. In W. Sailor, G. Dunlap, G. Sugai y R. H. Horner (Eds.), Handbook of positive behavior support (pp. 521-550). New York: Springer. 2009.
    
73. Langberg JM, Becker SB, Dvorsky MR. The Association Between Sluggish Cognitive Tempo and Academic Functioning in Youth with Attention-Deficit/Hyperactivity Disorder (ADHD). Journal of Abnormal Child Psychology. 2014;42: 91-103.
    
74. Barkley RA. Niños hiperactivos: cómo comprender y atender sus necesidades especiales. Barcelona: Paidós. 2002.
    
75. Barkley RA. ADHD and the nature of self-control. New York: Guilford. 2006.
    
76. Barkley RA. El manejo del TDAH en el aula: estrategias para el éxito. Ponencia presentada en el II Congreso Nacional de TDAH, Madrid. 2008.
    
77. Bull R, Scerif G. Executive function as a predictor of children’s mathematics ability: Inhibition, switching, and working memory. Developmental Neuropsychology. 2001;19: 273-293.
    
78. Bull R, Espy KA, Wiebe SA. Short-term memory, working memory, and executive functioning in preschoolers: longitudinal predictors of mathematical achievement at age 7 years. Dev Neuropsychol. 2008;33:205-28.
    
79. Espy KA, McDiarmid MM, Cwik MF, Stalets MM, Hamby A, Senn TE. The contribution of executive functions to emergent mathematic skills in preschool children. Dev Neuropsychol. 2004;26:465-86.
    
80. Van der Sluis, S., de Jong, P. F. & van der Leij, A. Executive functioning in children, and its relations with reasoning, reading, and arithmetic. Intelligence. 2007;35:427-449.
    
81. Geary DC, Hoard MK, Byrd-Craven J, Nugent L, Numtee C. Cognitive mechanisms underlying achievement deficits in children with mathematical learning disability. Child Dev. 2007;78:1343-59.
    
82. Pfiffner LJ, Yee Mikami A, Huang-Pollock C, Easterlin, B, Zalecki C, McBurnett K. A randomized, controlled trial of integrated home-school behavioral treatment for ADHD, predominantly inattentive type. Journal of the American Academy of Child and Adolescent Psychiatry. 2007;46(8):1041-1050.
    
83. Harrington KM, Waldman ID. Evaluating the utility of sluggish cognitive tempo in discriminating among DSM-IV ADHD subtypes. Journal of Abnormal Child Psychology. 2010;38(2): 173-184.
    
84. Burns GL, Servera M, Bernad MM, Carrillo JM, Cardo E. Distinctions between sluggish cognitive tempo, ADHD-IN, and depression symptom dimensions in Spanish first-grade children. Journal of Clinical Child and Adolescent Psychology: The Official Journal for the Society of Clinical Child and Adolescent Psychology, American Psychological Association, Division 2013;42(6):796-808.
    
85. Fenollar Cortés J, Servera M, Becker SP, Burns GL. External Validity of ADHD Inattention and Sluggish Cognitive Tempo Dimensions in Spanish Children With ADHD. Journal of Attention Disorders. 2014. http://doi.org/10.1177/1087054714548033
    
86. Becker SP, Luebbe AM, Joyce AM. The Child Concentration Inventory (CCI): Initial validation of a child self-report measure of sluggish cognitive tempo. Psychological Assessment. 2015;27(3):1037-1052.
    
87. Servera M, Bernad MDM, Carrillo JM, Collado S, Burns GL. Longitudinal Correlates of Sluggish Cognitive Tempo and ADHD-Inattention Symptom Dimensions with Spanish Children. Journal of Clinical Child and Adolescent Psychology: The Official Journal for the Society of Clinical Child and Adolescent Psychology, American Psychological Association, Division. 2015;53:1-10.
    
88. Burn GL, Lee S, Servera M, McBurnett K, Becker S.P. (n.d.). Child and Adolescent Behavior Inventory-Parent Version 1.0 (Vol. 2015). PullMan, WA: Author.
    
89. Lee S, Burns GL, Becker SP. Toward Establishing the Transcultural Validity of Sluggish Cognitive Tempo: Evidence From a Sample of South Korean Children. Journal of Clinical Child and Adolescent Psychology: The Official Journal for the Society of Clinical Child and Adolescent Psychology, American Psychological Association, Division. 2016;53:1-8.
    
90. Becker SP, Leopold DR, Burns GL, Jarrett MA, Langberg JM, Marshall SA, Willcutt EG. The Internal, External, and Diagnostic Validity of Sluggish Cognitive Tempo: A Meta-Analysis and Critical Review. Journal of the American Academy of Child and Adolescent Psychiatry. 2016;55(3):163-178.