Background: Writing is an important and complex skill, which could be enhanced by teaching students effective writing strategies such as outlining. Electronic outlining - integrated feature in Microsoft® Word -- has been shown to enhance students' writing performance. However, little is known about the optimal didactic approach for electronic outlining. Objective: This study examined the effects of learning to use electronic outlining either via observational learning or via learning-by-doing on students' argumentative writing performance. Methods: Students (N = 129, 10th-grade) were assigned with their complete class to one of three conditions: a control (traditional pen and paper outlines via learning-by-doing), outline (electronic outlines via learning-by-doing) or observation (electronic outlines via observational learning) condition. Students followed an argumentative writing lesson-series that differed across conditions in terms of planning strategies and didactic approaches used. To examine the influence of the different conditions on students' writing, argumentative texts were used as pre- and post-tests, and the quality was evaluated with an analytic assessment protocol. In addition, data regarding students' perceived mental effort and the organisation of the writing process were collected. Finally, students' attitudes towards electronic outlining were assessed. Results and Conclusion: Although the overall text structure had improved after the lesson series, no significant differences were found between conditions. Electronic outlining increased the total amount of time dedicated to the texts as well as the revision ratio. Students in the observation condition showed a higher pause ratio and a lower fluency on the post-test as compared to students who learned by doing (both control and outline conditions). With regard to perceived mental effort, students in the outline and control conditions perceived significant decreases over tasks, as opposed to those in the observation condition. In conclusion, the self-reports indicate that students in the outline condition appropriated electronic outlining significantly better than those in the observation condition, suggesting that practice enhanced students' appropriation of electronic outlining.