The design of effective interventions for antisocial adolescents has been greatly influenced by research-based developmental theories. However, randomized clinical trials (RCTs) demonstrating effectiveness of these treatments have contributed minimally to alterations and refinements of these theories. In this article, nine guidelines for research that may enhance the contributions of RCTs to developmental theory are proposed: (1) use mediational analyses to test and refine theories of change; (2) use moderator analyses to test differential pathways to change; (3) assess change processes separately for different types of antisocial behavior; (4) use constructive and dismantling designs to isolate effects of intervention components on targeted mediators and outcomes; (5) assess the time-sensitive nature of change mechanisms with theoretically relevant spacing of multiple assessments and long-term follow-ups; (6) expand the nomological net of developmental theories by assessing intervention effects on nontargeted constructs; (7) use RCTs to disentangle direction of effects questions in developmental theories; (8) conduct secondary analyses of RCTs to assess extra-treatment influences on antisocial behavior; and (9) assess the generalizability of mediator and moderator effects. Use of these guidelines may promote a recursive and iterative relationship between RCTs and theory building. Improved developmental theories may yield more effective interventions, and theory-testing interventions may engender more comprehensive and better informed theories.