Two major transitions ” initial school entry and transition to middle school ” are emphasized as the points in development most amenable to preventing conduct disorder. As a complement to Reid's analysis of the child and family foci for prevention efforts, this paper discusses the importance of considering social context factors in prevention. In the early school years, peers inadvertently reinforce aggressive and coercive behavior and, thus, contribute to the coercive cycle Patterson describes in families. Middle schools in inner-city contexts have peer social network characteristics that also support delinquent and violent behavior more directly, in contrast to the general suppositions of social control theories of delinquency. The impact of neighborhoods and the larger societal tolerance of violence reflected in the media are also discussed. Prevention strategies for addressing these contextual factors at both developmental periods are outlined in the paper. © 1993, Cambridge University Press. All rights reserved.