Neurocognitive heterogeneity is increasingly recognized as a valid phenomenon in ADHD, with most estimates suggesting that executive dysfunction is present in only about 33%-50% of these children. However, recent critiques question the veracity of these estimates because our understanding of executive functioning in ADHD is based, in large part, on data from single tasks developed to detect gross neurological impairment rather than the specific executive processes hypothesized to underlie the ADHD phenotype. The current study is the first to comprehensively assess heterogeneity in all three primary executive functions in ADHD using a criterion battery that includes multiple tests per construct (working memory, inhibitory control, set shifting). Children ages 8-13 (M = 10.37, SD = 1.39) with and without ADHD (N = 136; 64 girls; 62% Caucasian/Non-Hispanic) completed a counterbalanced series of executive function tests. Accounting for task unreliability, results indicated significantly improved sensitivity and specificity relative to prior estimates, with 89% of children with ADHD demonstrating objectively-defined impairment on at least one executive function (62% impaired working memory, 27% impaired inhibitory control, 38% impaired set shifting; 54% impaired on one executive function, 35% impaired on two or all three executive functions). Children with working memory deficits showed higher parent- and teacher-reported ADHD inattentive and hyperactive/impulsive symptoms (BF = 5.23 × 10), and were slightly younger (BF = 11.35) than children without working memory deficits. Children with vs. without set shifting or inhibitory control deficits did not differ on ADHD symptoms, age, gender, IQ, SES, or medication status. Taken together, these findings confirm that ADHD is characterized by neurocognitive heterogeneity, while suggesting that contemporary, cognitively-informed criteria may provide improved precision for identifying a smaller number of neuropsychologically-impaired subtypes than previously described.

Objective: Executive function deficits are well-established in ADHD. Unfortunately, replicated evidence indicates that executive function training for ADHD has been largely unsuccessful. We hypothesized that this may reflect insufficient targeting, such that extant protocols do not sufficiently and specifically target the neurocognitive systems associated with phenotypic ADHD behaviors/impairments. Method: Children with ADHD ages 8–12 (M = 10.41, SD = 1.46; 12 girls; 74% Caucasian/Non-Hispanic) were randomized with allocation concealment to either central executive training (CET; n = 25) or newly developed inhibitory control training (ICT; n = 29). Detailed data analytic plans were preregistered. Results: Both treatments were feasible/acceptable based on training duration, child-reported ease of use, and parent-reported high satisfaction. CET was superior to ICT for improving its primary intervention targets: phonological and visuospatial working memory (d = 0.70–0.84). CET was also superior to ICT for improving go/no-go (d = 0.84) but not stop-signal inhibition. Mechanisms of change analyses indicated that CET-related working memory improvements produced significant reductions in the primary clinical endpoints (objectively assessed hyperactivity) during working memory and inhibition testing (indirect effects: β ≥ −.11; 95% CIs exclude 0.0). CET was also superior to ICT on 3 of 4 secondary clinical endpoints (blinded teacher-rated ADHD symptoms; d = 0.46–0.70 vs. 0.16–0.42) and 2 of 4 feasibility/acceptability clinical endpoints (parent-reported ADHD symptoms; d = 0.96–1.42 vs. 0.45–0.65). CET-related gains were maintained at 2–4 month follow-up; ICT-related gains were maintained for attention problems but not hyperactivity/impulsivity per parent report. Conclusions: Results support the use of CET for treating executive function deficits and targeting ADHD behavioral symptoms in children with ADHD. Findings for ICT were mixed at best and indicate the need for continued development/study.

Objective Working memory deficits have been linked experimentally and developmentally with ADHD-related symptoms/impairments. Unfortunately, substantial evidence indicates that extant working memory training programs fail to improve these symptoms/impairments. We hypothesized that this discrepancy may reflect insufficient targeting, such that extant protocols do not adequately engage the specific working memory components linked with the disorder’s behavioral/functional impairments. Method The current study describes the development, empirical basis, and initial testing of central executive training (CET) relative to gold-standard behavioral parent training (BPT). Children with ADHD ages 8–13 (M=10.43, SD=1.59; 21 girls; 76% Caucasian/Non-Hispanic) were treated using BPT (n=27) or CET (n=27). Detailed data analytic plans for the pre/post design were preregistered. Primary outcomes included phonological and visuospatial working memory, and secondary outcomes included actigraphy during working memory testing and two distal far-transfer tasks. Multiple feasibility/acceptability measures were included. Results The BPT and CET samples did not differ on any pre-treatment characteristics. CET was rated as highly acceptable by children, and was equivalent to BPT in terms of feasibility/acceptability as evidenced by parent-reported high satisfaction, low barriers to participation, and large ADHD symptom reductions. CET was superior to BPT for improving working memory (group x time d=1.06) as hypothesized. CET was also superior to BPT for reducing actigraph-measured hyperactivity during visuospatial working memory testing and both distal far-transfer tasks (group x time d=0.74). Conclusions Results provide strong support for continued testing of CET and, if replicated, would support recent hypotheses that next-generation ADHD cognitive training protocols may overcome current limitations via improved targeting.

Objective: Executive functions are commonly measured using rating scales and performance tests. However, replicated evidence indicates weak/nonsignificant cross-method associations that suggest divergent rather than convergent validity. The current study is the first to investigate the relative concurrent and predictive validities of executive function tests and ratings using (a) multiple gold-standard performance tests, (b) multiple standardized rating scales completed by multiple informants, and (c) both performance-based and ratings-based assessment of academic achievement-a key functional outcome with strong theoretical links to executive function. Method: A well-characterized sample of 136 children oversampled for ADHD and other forms of child psychopathology associated with executive dysfunction (ages 8 -13; 68% Caucasian/non-Hispanic) completed a counterbalanced series of executive function and academic tests. Parents/teachers completed executive function ratings; teachers also rated children's academic performance. Results: The executive function tests/ratings association was modest (r ϭ .30) and significantly lower than the academic tests/ratings association (r ϭ .63). Relative to ratings, executive function tests showed significantly higher cross-method predictive validity and significantly better within-method prediction; executive function ratings failed to demonstrate improved within-method prediction. Both methods uniquely predicted academic tests and ratings. Conclusion: These findings replicate prior evidence that executive function tests and ratings cannot be used interchangeably as executive function measures in research and clinical applications, while suggesting that executive function tests may have superior validity for predicting academic behavior/achievement.

Reading problems are common in children with ADHD and show strong covariation with these children's underdeveloped working memory abilities. In contrast, working memory training does not appear to improve reading performance for children with ADHD or neurotypical children. The current study bridges the gap between these conflicting findings, and combines dual-task methodology with Bayesian modeling to examine the role of working memory for explaining ADHD-related reading problems. Children ages 8-13 (M = 10.50, SD = 1.59) with and without ADHD (N = 78; 29 girls; 63% Caucasian/Non-Hispanic) completed a counterbalanced series of reading tasks that systematically manipulated concurrent working memory demands. Adding working memory demands produced disproportionate decrements in reading comprehension for children with ADHD (d = -0.67) relative to Non-ADHD children (d = -0.18); comprehension was significantly reduced in both groups when working memory demands were increased. These effects were robust to controls for foundational reading skills (decoding, sight word vocabulary) and comorbid reading disability. Concurrent working memory demands did not slow reading speed for either group. The ADHD group showed lower comprehension (d = 1.02) and speed (d = 0.69) even before adding working memory demands beyond those inherently required for reading. Exploratory conditional effects analyses indicated that underdeveloped working memory overlapped with 41% (comprehension) and 85% (speed) of these between-group differences. Reading problems in ADHD appear attributable, at least in part, to their underdeveloped working memory abilities. Combined with prior cross-sectional and longitudinal findings, the current experimental evidence positions working memory as a potential causal mechanism that is necessary but not sufficient for effectively understanding written language.