This study adopted a sequential explanatory mixed-methods approach and followed the Vygotskian social-constructivist theory of learning to explore the impact of wiki-mediated collaborative writing on English as a foreign language (EFL) students’ writing performance, writing self-regulation, and writing self-efficacy. To this aim, two intact classes were selected and randomly assigned to experimental group with 35 EFL students and control group with 32 EFL students. Over the period of one term (almost 12 ninety-minute sessions), the students were aimed to co-construct and improve their writing performance, writing self-regulation, and writing self-efficacy through collaborative writing activities. In the experimental group, the EFL students received wiki-mediated collaborative writing instruction, while in the control group the EFL students experienced face-to-face (non-wiki) collaborative writing instruction. Two timed writing tasks, second language writing self-regulation and writing self-efficacy scales, and an individual semi-structured interview were conducted to collect the required data. Additionally, the types and frequencies of the students’ writing mediations in the wiki-mediated collaborative writing group were identified. The quantitative data were analysed using paired samples t-tests and one-way ANCOVA, and language-related episodes and thematic analyses were applied to analyse the qualitative data. The quantitative data analyses indicated that both wiki-mediated and non-wiki collaborative writing instructions improved the writing performance, writing self-regulation, and writing self-efficacy of the EFL students. The quantitative data analyses also showed that the EFL students in wiki-mediated collaborative writing group outperformed those in the non-wiki collaborative writing group. The qualitative data analyses uncovered a number of peer writing mediations contributing to the EFL students’ writing content (i.e. clarity of the produced message), writing organisation (i.e. sequencing of information), and language use (i.e. grammar, lexicon, & writing mechanics) in the wiki space. The qualitative data analyses further indicated the EFL students’ positive attitudes and perceptions towards wiki-mediated collaborative writing. Pedagogical implications are further discussed.
