My research focuses on using psychometric models to understand neurodevelopmental changes in executive functions. These cognitive abilities, such as reasoning, problem solving and goal management, develop rapidly during adolescence and often show steep decline in old age. However, the neurocognitive changes that underlie these important processes are poorly understood, and many key questions are unresolved: What represents optimal brain development? How do changes in brain structure and function interact across the lifespan? Can people recruit additional neural resources to maintain performance? What sets apart people who maintain cognitive abilities into old age? To understand these questions, we must study the dynamics of development: how does brain function and structure change across the lifespan, and how does this affect our higher cognitive abilities? I approach these questions using psychometric techniques in large-sample, multimodal, longitudinal datasets.