The present study is a large-scale randomized trial testing the efficacy of a family-school partnership model (i.e., conjoint behavioral consultation) for promoting behavioral competence and decreasing problem behaviors of students identified by their teachers as disruptive. The focus of this study is on student behavioral outcomes and the potential role of parent-teacher relationships as a mediating variable. Two hundred seven students, from 82 classrooms, and their families and teachers participated. Results indicated that, relative to the control group, students in the conjoint behavioral consultation condition demonstrated greater increases in adaptive behaviors and social skills over the 8-week intervention period. Compared to teachers in the control group, those in the experimental conjoint behavioral consultation condition demonstrated significantly greater change in their reported relationships with parents. Furthermore, improvements in teacher-reported relationships with parents mediated the effects of conjoint behavioral consultation on positive changes in children's behaviors. Interpretation and implications of these findings are discussed. (Contains 4 tables and 2 figures.)