Abstract Children show dramatic developments in executive functioning, the goal-directed processes that support flexible adaptation of behavior in response to changing circumstances. Variations in executive functioning during childhood predict important life outcomes across childhood and adolescence into adulthood, including behavioral, health, socioemotional, and academic outcomes. Executive functions are impaired in clinical disorders including depression, ADHD, autism and schizophrenia. Discoveries about executive functioning are thus of fundamental importance to understanding and promoting precursors to optimal mental, behavioral, and physical development. Given this significance, many studies and intervention attempts have focused on understanding and supporting children’s capacity to engage executive functions. However, children adaptively coordinate whether to engage executive functions based on a variety of factors beyond capacity. Children may elect not to engage executive functioning because it is unlikely to pay off or to be worth the effort, or is not valued by others around them. These choices can have cascading effects, supporting the development of habits that make it harder (or easier) to engage executive functions in the future. Variations in executive functioning and associated outcomes across individuals and diverse groups may reflect such adaptations. This project thus investigates how executive functions are adaptively coordinated across development to match environmental demands, how these adaptations can be harnessed during sensitive time periods to develop effective interventions, and how these adaptations lead to cascading effects that are important to healthy development. We systematically investigate these underexplored processes across three key domains relating to executive function: A) temporal dynamics, B) delay of gratification, and C) response inhibition and mental effort. Within each domain, we test three hypotheses: Children’s experiences, habits, and adaptations to their unique environments shape their decisions to engage executive functioning, such that variations in executive function can be understood in terms of matches or mismatches between demands of the current environment and the way children have previously learned to engage executive function (Aim 1). Interventions will be effective if they increase children’s decisions to engage executive functions and build habits around engaging executive functions in relevant contexts (Aim 2). Children’s adaptations in their executive functioning have cascading effects on their learning and academic achievement, challenge-seeking, problem behaviors, and other executive functions, leading to benefits and costs and explaining links between executive function and healthy development (Aim 3). These multi-component studies will leverage behavioral, neurophysiological, and self- and parent-report measures to yield rich, well-powered, longitudinal datasets and advance an...