Although intervention procedures exist for improving elementary-aged students’ writing fluency skills, less is known about how their writing self-efficacy develops upon participating in these procedures. In this study, 117 second grade students participated in an evidence-based performance feedback writing intervention. Students reported higher levels of self-efficacy in their writing abilities after participating in the intervention than they did at baseline. Although their experiences with task mastery and positive feedback did not impact their writing self-efficacy, the effort they put forth during the intervention was a significant predictor. These results may provide initial guidance for the development of students’ self-efficacy in the context of school-based interventions, and they have specific implications for how the performance feedback intervention procedures may be refined to more systematically target students’ task effort in future research.