This article, the third in a series of articles from the National Association for Sport and Physical Education (NASPE) sport structures, explains how the following two scenarios relate to Domain 4 Standards: (1) two adolescent boys have different baseball throwing skill levels, even though they have been on the same team for the past four years; and (2) two 12-year old girls who have the same coach and receive the same instruction, develop their skills differently after only six weeks of practicing tennis. What explains the difference? What should the coach know and be able to do in each scenario? This article demonstrates how each of the following Domain 4 Standards offers some answers: (1) Standard 14--Coaches will demonstrate knowledge of the developmental changes that occur as athletes move from youth to adulthood and how these changes influence the learning and performance of motor skills; (2) Standard 15--Coaches will provide individualized and differentiated instruction to develop sport-specific motor skills based on developmental status of athletes; and (3) Standard 16--Coaches will facilitate the social and emotional growth of athletes which will support participation in physical activity throughout the lifespan. The article concludes that with an understanding of basic growth and developmental characteristics, coaches will be able to create a caring and positive sport experiences for their athletes that that encourages growth of all participants.