Writing is an important language skill, and learning to write is not an easy endeavour, especially for English as a foreign language (EFL) students. An effective EFL writing instruction, therefore, plays a significant role in helping EFL students deal with writing problems efficiently and approach writing tasks effectively. Based on this premise, the present study aims at investigating the effect of two alternative writing approaches, process and product, on Moroccan EFL students' writing performance to find out which of these approaches is more effective. It explores process writing instruction based on Hayes' (2012) recent model that responded to both critiques of the 1980-s original model of Flower and Hayes and to new ideas, which adds more layers to EFL writing research and instruction. To this end, the participants were divided into two groups, A and B, and they all took a writing pre-test before the treatment. For three months (two hours per week), group A students received academic argumentative writing instruction that was product-oriented, while group B students were taught academic argumentative writing based on Hayes' (2012) process writing model. After the treatment, all participants took a writing posttest. The analysis of the collected data revealed that group B participants showed a significant improvement in their compositions compared to their group A counterparts, which provides evidence that the process-oriented approach is more effective in enhancing EFL writing than the product-oriented approach. In the light of these findings, some pedagogical recommendations were suggested.