Background  Associations among cognitive development and intrapersonal and environmental characteristics were investigated for 89 longitudinal study participants with Down syndrome to understand developmental patterns associated with cognitive strengths and weaknesses.

Materials and Methods  Subtest scores of the Stanford‐Binet IV collected between ages 4–30 years were analysed in multilevel models of age‐related change. Predictor variables were systematically entered into the models to identify associations with development for each subtest.

Results  Temperament, maternal education, medical conditions and school experiences were associated with cognitive differences. Additional associations with rate of development were detected for negative mood, persistence, maternal education level and elementary school experience for several subtests.

Conclusions  Early cognitive advantage and consistent opportunities to learn academic content appear to facilitate cognitive development, although this latter was confounded with ability and maternal education in this study. Data presented endorse research into interventions that enhance verbal and problem solving environments through‐out early and middle childhood and target reductions in negative affect in relation to supporting cognitive development for individuals with Down syndrome.