This article reports the results of a sequential explanatory mixed-methods approach to explore the impact of online peer-editing using Google Docs and peer-editing in a face-to-face classroom on EFL learners' academic writing skills. As the study adopted a quasi-experimental design, two intact classes, each with ten EFL learners, attending an IELTS course at a language institute in Sanandaj, Iran, were selected as the participants. IELTS academic writing task 1 and task 2 were used to assess the learners' academic writing skills, and a semi-structured interview was conducted to explore the learners' perceptions towards the impact of online peer-editing on academic writing skills. A paired-samples t-test, an independent-samples t-test, and a one-way MANCOVA were used to analyse the quantitative data. The results indicated that peer-editing both through using Google Docs and in the face-to-face classroom significantly developed the learners' academic writing skills, and that the former outperformed the latter both in the short and long term. Moreover, after controlling for the pre-tests, the two groups performed differently on the four areas of academic writing on both the post- and delayed post-tests. Thematic analysis, used to analyse the qualitative data, highlighted the learners' positive perceptions towards the impact of online peer-editing on academic writing skills.