This article evaluates the efficacy of the Oregon model of Parent Management Training (PMTO) in the stepfamily context. Sixty-seven of 110 participants in the Marriage and Parenting in Stepfamilies (MAPS) program received a PMTO-based intervention. Participants in the randomly assigned experimental group displayed a large effect in benefits to effective parenting practices with resultant decreases in child noncompliance and in home and school problem behaviors. MAPS findings replicate and extend those of the Oregon Divorce Study with single mothers while employing a similar multiple-method, multiple-measure randomized design, with Intent-to-Treat and structural equation modeling analyses. We discuss direct and indirect effects on distal outcomes and the generalizability of PMTO to differing family contexts.