This study was designed to identify, through mediation analysis, potential causal mechanisms by which procedures of self-regulated learning increase the efficaciousness of teaching young students strategies for writing stories. In a randomized controlled trial with 3 measurement points (pretest, posttest, maintenance), 117 fourth graders either received self-regulatory writing strategies training or were taught writing strategies without self-regulation procedures. Path analyses indicated that relative to teaching writing strategies alone, teaching strategies in tandem with self-regulation procedures improved students' skills of planning and revising stories and thereby enhanced the quality of the resulting stories. Self-regulated learning also enhanced students' knowledge about good writing and strengthened their self-efficacy beliefs, which both had a positive effect on the use of the learned strategies while planning narratives. (Contains 6 tables, 2 figures and 4 footnotes.)