Developmental milestones as early indicators of twice-exceptionality

Twice-exceptional individuals are those who have high cognitive ability in one or more areas, but also have a diagnosed disability. The needs of these individuals likely differ from those with high cognitive ability without a disability and those who solely have a disability. Intervening early can offer exceptional benefits for twice-exceptional individuals, but this has proved challenging due to the high cognitive abilities masking disabilities. This study explores if parent-reported developmental milestones can predict the number of disabilities diagnosed for an individual, including Autism Spectrum Disorder (ASD), Attention-Deficit/Hyperactivity Disorder (ADHD), and Specific Learning Disorder (SLD). Using a clinical sample of about 1,300 individuals, we used a Bayesian cumulative logistic model to explore if developmental milestones can predict the number of diagnoses after controlling for IQ and age. Study results showed that when an individual began to count and read informed predictions for the number of future diagnoses in the clinical sample. Implications for future study and practitioners are discussed in further detail.