This paper has investigated the importance of explicit instruction and collaborative writing on (a) argumentative writing performance and (b) self-efficacy for writing of secondary school students. This intervention study additionally aimed to evaluate the effectiveness of alternating between individual and collaborative writing throughout the writing process (planning collaboratively, writing individually, revising collaboratively, and rewriting individually). A cluster randomized control trial (CRT) design was opted for. To investigate the effect of the intervention on secondary school students' writing performance and self-efficacy for writing, multilevel analyses were performed. It was found that the presence of explicit instruction in combination with collaborative writing is positively related to argumentative writing performance and self-efficacy for writing. Alternating between individual and collaborative writing was not significantly different from collaborating throughout all phases of the writing process. More in-depth research into the quality of collaboration is, however, needed to gain insight into the interaction processes and writing processes that take place during collaborative writing.