Writing is a complex task. Its development depends in large part on changes that occur in children’s strategic behavior, knowledge, and motivation. In the present study, the effectiveness of an instructional model, Self-Regulated Strategy Development (SRSD), designed to foster development in each of these areas, was examined. Adding a peer support component to SRSD instruction to facilitate maintenance and generalization was also examined. Struggling, third grade writers, the majority of whom were minority students attending schools that served primarily low-income families, received SRSD instruction focused primarily on learning writing strategies and knowledge for planning and composing stories and persuasive essays. These students wrote longer, more complete, and qualitatively better papers for both of these genres than peers in the comparison condition (Writers’ Workshop). These effects were maintained over time for story writing and generalized to a third uninstructed genre, informative writing. SRSD instruction boosted students’ knowledge about writing as well. The peer support component augmented SRSD instruction by increasing students’ knowledge of planning and enhancing generalization to informative and narrative writing. In contrast, self-efficacy for writing was not influenced by either SRSD condition (with or without peer support).