This intervention study aimed to test the effect of writing process feedback. Sixty-five Grade 10 students received a personal report based on keystroke logging data, including information on several writing process aspects. Participants compared their writing process to exemplar processes of equally scoring (position-setting condition) or higher-scoring students (feed-forward condition). The effect of the feedback on writing performance and process was compared to a national baseline study. Results showed that feed-forward process feedback had an effect on text quality comparable to one grade of regular schooling. The feedback had an effect on production, pausing, revision, and source use, which indicates that it supported participants in self-regulating their writing process. Additionally, we explored the students' perception of the feedback to get an insight into its strengths and weaknesses. This study shows the potential of writing process feedback and discusses pedagogical implications and options for future research.