Findings showed the following distribution of involvement in activities: sports outside of school (44 percent), sports teams at school (42 percent), volunteer work (41 percent), clubs outside of school (38 percent), musical instruments (33 percent), clubs at school (32 percent), leadership activities (24 percent), and drama/fine arts (21 percent). Gender differences and similarities were found in the types of activities selected. Fifteen percent of respondents reported no involvement in any of the eight activities (13 percent of boys and 17 percent of girls). The other youth reported an average involvement in two or three activities. Consistent with previous research, this study found that the number of activities (breadth) had more robust links with each of the developmental measures than did the frequency of involvement (intensity). This suggests that youth benefit more from the diversity of activities than from the frequency of their participation in a given activity. Interactions between breadth and intensity only influenced the development measure of well-being. Both breadth and intensity were positively related to each development measure. Findings were consistent across age levels. The sample consisted of students from 25 high schools in a school district in Ontario, Canada, as part of the Youth Lifestyle Choices Community-University Research Alliance project, a 23-page self-report questionnaire was administered to students in classrooms. The questionnaire obtained information on demographics, involvement in eight domains of activity, risk behaviors (substance use, sexual activity, minor delinquent acts, and aggressive behavior), well-being, academic orientation, and social/interpersonal functioning. 5 tables and 57 references