Writing in history places high demands on students and is a skill that requires explicit instruction. Therefore, teachers need to be able to teach this in an effective way. In this study, the writing-instruction was designed by a teacher, instead of researchers, as part of a professional development program in the Netherlands. The lessons combined writing and historical reasoning instruction, based on principles of effective writing instruction, including strategy-instruction, modeling, prewriting, and peer-interaction. The effects of these lessons were investigated in a small-scale pilot study, which consisted of a pre-test post-test quasi-experimental design, in which eighty-nine 11th grade students participated (39 in the treatment condition and 50 in the comparison condition). Dependent measures included text quality, writing process measures, students' knowledge of writing and their self-efficacy. Students in the treatment condition wrote longer and higher quality texts, spent more time writing, paused more while writing and their knowledge of writing was higher at post-test than for students in the comparison condition. No effects were found for selfefficacy. Furthermore, significant correlations were found between text quality and writing process measures, but not for knowledge of writing and self-efficacy. Overall, the effectiveness of this teacher-designed intervention seemed satisfactory, as it resulted in greater knowledge of writing and better-quality writing in his history classes.