In a few years, the United States is going to have the largest number of teenagers it has ever had; at the same time, crime among teenagers is rising, and the recreational and learning activities and jobs that teenagers need for positive development are becoming scarcer in inner city and rural areas. Efforts in youth programs during the past 25 years reveal the following: (1) early childhood and adolescent programs often have strong positive effects, but these effects generally do not last into adulthood; (2) programs for older teenagers and young adults who have already exhibited behavioral and/or performance problems also often show good short-term effects, but only a very few achieve long-term impacts on social behavior and labor market performance; and (3) successful social intervention for young children and early teens is rooted in creating strong relationships with adults and in providing engaging and positive activities. Recommendations for the future include the following: (1) continue a steady and measured expansion of investment in early childhood programs, focusing on the quality and intensity of adult time spent with young children; (2) do not continue massive federally regulated job placement programs for older teens and young adults based solely on local poverty and employment rates, but rather use a work force development block grant strategy and encourage state investment in local organizations that can become brokers between poor communities and area employers; and (3) increase federal investment in building a stronger web of basic local supports for teenagers. Instead of complex, problem-oriented programs and services, public policy should encourage basic supports (sustained adult attention and guidance and a variety of positive activities) for young people. (Contains a list of Public/Private Ventures publications, with instructions and cost for ordering.) (KC)