Cognition and maths in children referred for ADHD assessment
Attention Deficit Hyperactivity Disorder (ADHD) is a lifelong neurodevelopmental disorder. ADHD symptoms manifest as persistent inattention, hyperactivity, and/or impulsivity. Children with ADHD also show pervasive difficulties in cognitive processes including Executive Functions, memory, and processing speed – processes hypothesised to underpin academic success. Many children with ADHD struggle with maths, as demonstrated by lower levels of attainment and higher incidence of maths learning difficulties. Maths abilities predict a range of outcomes in adulthood and therefore represent a particularly important area of investigation in this population. However, much of the previous research relies on broad attainment tests to explore maths performance. Such tests risk masking more intricate sources of maths difficulties. Specifically, three maths components are proposed to support broad maths achievement in children: factual knowledge, conceptual understanding, and procedural skill. These skills have not yet been explored comprehensively in children with ADHD. Not all children with ADHD show difficulties with maths and some perform similarly to their neurotypical peers. The source of this within group variability has previously been attributed to differences in behavioural symptom presentations, such as inattention. Given that behavioural manifestations are closely linked to differences in neurocognitive abilities, which are also notoriously diverse in ADHD, cognitive mechanisms could offer a better explanation for heterogeneity in maths performance. Keeping the componential nature of maths skills in mind, the broad aim of this thesis was to conduct a comprehensive investigation into their relationship with behavioural and cognitive processes in a clinical ADHD population. Exploring how performance across these components relates to behavioural and cognitive functioning in ADHD can help inform pathways of risk for maths difficulties and act as a steppingstone to devising educational interventions. Following the General Introduction, Chapter 2 includes a systematic review of existing literature addressing the association between previously implicated cognitive processes and maths performance in ADHD. To date, studies on the relationship between cognition and maths in ADHD have not been systematically reviewed making it difficult to appraise research in this area. The results showed a positive association between cognition and maths performance in this population. However, very few studies met inclusion criteria and those that did, only assessed a limited number of relevant cognitive domains. The results of this chapter demonstrate a lack of research into the relationship between cognition and maths in clinical ADHD and, via quality appraisal, highlight key methodological considerations for future research. Chapter 3 contains the General Methodology which explores the methodological decisions employed for the remaining study chapters such as participant inclusion and materials used. This chapter also provides information on procedures used, ethics, participant characteristics, missing data, sample size, and data preparation. Chapter 4 comprises a comprehensive investigation of cognition, behaviour, and maths in 44 drug naïve children on the waiting list for ADHD evaluation at Child and Adolescent Mental Health Services. The results showed that cognition, rather than ADHD symptoms, correlated with both standardised maths attainment scores and more specific components of maths skills. In particular, verbal, and visuospatial aspects of memory functioning showed the strongest associations with maths across the board. This suggests that cognitive processes, rather than clinical ADHD symptoms, are more informative for maths performance in children with clinically high ADHD symptoms and represent viable targets for future research on maths interventions. This chapter also demonstrated high rates of co-occurrence with other neurodevelopmental disorders which must be considered when characterising ADHD samples. Chapter 5 built on the richness of the clinical characterisation in the preceding chapter, which found that around half of the sample showed motor difficulties indicative of Developmental Coordination Disorder (DCD). Specifically, this study divided the sample into two groups – one with high ADHD and DCD symptoms (ADHD + co-occurring motor difficulties) and one who scored lower on the DCD assessment screener (ADHD-only). The results showed that these groups were comparable in terms of maths performance and in many of the cognitive tasks. However, the ADHD + co-occurring motor difficulties group showed significantly poorer performance on visuospatial WM than the ADHD-only group. This highlighted visuospatial WM as a clinically informative and distinguishing feature of children with concurrently high DCD symptoms. Overall, the strength of associations between cognitive processes and maths skills did not differ. This further pointed to cognitive dimensions as more informative mechanisms in relation to maths, than that of diagnostic symptomatology. The final study chapter, Chapter 6, compared a traditional categorical grouping approach (i.e., clinical ADHD vs no clinical ADHD diagnosis) to that of a data-driven grouping approach (i.e., groups based on children’s cognitive data). This chapter demonstrated that a categorical diagnostic approach was not informative of children’s maths outcomes. By contrast, the data-driven approaches, which grouped children using relevant cognitive performance, generated meaningful cognitive subgroups which could be differentiated on their maths, as well as intelligence scores. This suggests that cognitive patterns of performance, rather than children’s diagnostic outcomes, are more informative for identifying meaningful groups of struggling learners. Collectively, the current thesis is the first to provide a comprehensive investigation of maths skills in a clinically referred and drug naïve sample of children with high ADHD symptoms. Throughout this thesis, practical and theoretical implications for future work in ADHD are discussed.