The contributions of motor skill and cognition (decision making and knowledge) to sport performance change across age, expertise, and sports. Knowing how to execute a skill is a prerequisite for efficient and effective execution. As skill execution improves, the cognitive aspects of motor execution become automated. For low-strategy sports (e.g., swimming) variables such as physical size and ability combine with motor skill to determine expertise. In highstrategy sports (e.g., basketball) cognition remains an important variable in game performance. The performer must know what to do and then be able to execute the plan. Knowledge and decision making should not limit the development of expertise. Specific strategies for coaches and teachers may facilitate the development of expertise in children and adolescents.