Is the Diagnosis of ADHD Influenced by Time of Entry to School? An Examination of Clinical, Familial, and Functional Correlates in Children at Early and Late Entry Points

Objective: The authors examined the proposed immaturity hypothesis, which suggests that younger children may have developmental immaturity and not ADHD, using data from a large, clinically referred population of individuals with and without ADHD. Method: The sample consisted of individuals with and without an ADHD diagnosis, ascertained from ongoing studies in our laboratory, born in August (Younger Cohort N = 562) and born in September (Older Cohort N = 529). The authors compared studywide diagnosis rates of ADHD, ADHD familiality patterns, ADHD symptoms, psychiatric comorbidity, and functional impairments between the two cohorts. Results: Studywide rates of ADHD diagnosis, ADHD-associated symptoms, ADHD-associated impairments, ADHD-associated comorbid disorders, and familiality were similar in the two age cohorts. Conclusion: Results showed that ADHD-associated familial, clinical, and functional correlates are similar irrespective of age at entry to school, indicating that when ADHD symptoms are present, a diagnosis of ADHD should be considered rather than attributing these symptoms to developmental immaturity.