In this design study, we designed an instructional unit open to contextual modifications with the aim of fostering secondary school students' philosophical writing. Three philosophy teachers developed innovative source-based writing tasks and provided discipline-specific writing strategy instruction in their 10th grade class. In this study, we focused on change. We explored teachers' interaction with the instructional design and studied teachers' views on how the intervention had changed their practice since a change of beliefs is crucial to successful, durable innovation of teaching. Moreover, we studied the effects of the changed practice, by exploring change in students' writing. An external jury analyzed students' texts to determine students' actual learning achievements. Teachers' insights into student progress were obtained from reflective interviews that featured comparisons between the observed and expected results. The results showed that teachers judged the design to be feasible, valid, and effective for students' philosophical writing development. After the intervention, students' texts showed similar or even more independent philosophical thinking than before, while the tasks became more complex. Implementation drove teachers to contemplate writing instruction, indicating a change in their belief system, which is necessary for genuine improvement in teacher practice.

Source-based writing is a common but difficult task in history and philosophy. Students are usually taught how to write a good text in language classes. However, it is also important to address discipline-specificity in writing, a topic likely to be taught by content teachers. In order to design discipline-specific writing instruction, research needs to identify which reading and writing activities during the source-based writing process affect students’ thought process quality and text quality, as assessed by content teachers. We conducted a think-aloud study with 15 (11th grade) students who performed two source-based writing assignments, each representative of its discipline. From the data, we derived 11 activities, which we analyzed for duration, frequency, and time of occurrence. Results showed that the disciplines required different approaches to writing. For philosophy, the writing process was dominant and influenced quality, leading us to conclude that philosophical thinking and writing are intertwined. For history, the planning process appeared to be paramount, but it influenced text quality only and not the quality of the thought process. In other words, historical thinking and writing appear to be separate processes. Our findings can be used to develop strategy instruction that reinforces better writing, adapted to discipline-specific writing processes.