Notably, there were no cross-lagged associations between the ages of 3–4 and 4–5 years. It is possible that domains such as working memory, inhibitory control and executive functions, that are associated with ADHD symptoms, may not be adequately developed by the age of 3–4 years; or that they are not adequately assessed by the NEPSY in that age-range. NEPSY has poorer reliability in very young children and some subtests differ between preschoolers and school-aged children (Korkman et al., 1998); these differences may have impacted our results in unmeasured ways. Alternatively, early neuropsychological deficits may be significantly associated with escalation in symptoms only when children face demands from formal school settings.
