In this article, the authors consider the conditions under which participation in organized out-of-school activities contributes to positive development. They center their discussion on what is known about the "processes" in organized activities that affect the development of young persons. By using the term "organized activities", they wish to make clear that their focus is on out-of-school activities characterized by structure, adult supervision, and an emphasis on skill building. The authors begin by highlighting some of the basic risks for youth whose out-of-school experience involves a great deal of unstructured leisure. They then contrast these risks with the developmental opportunities provided through participation in organized out-of-school activities. In doing so, they outline the features of organized activities thought to account for their developmental impact and review the existing literature on activity-related processes and the psychosocial adjustment of young persons. Throughout this article, the authors discuss implications of this knowledge base for developing effective out-of-school activities and suggest areas for future research in the field. (Contains 65 notes.)