The potential of wikis for learning has recently begun to capture the attention of English as a second/foreign language (ESL/EFL) research. While students' collaboration, attention to form, and perceptions of wikis in document mode have been widely addressed in previous research, the educational value of wikis used in thread mode, as discussion forums, has been rarely explored. In an attempt to fill this gap in the literature, the present case study reports on 20 EFL learners' contribution to a classroom wiki during a 9-week writing course. The wiki is applied as a forum for out-of-classroom discussions regarding English writing. Focus is placed upon the type and degree of students' contribution to the wiki as well as their attention to form while publishing their messages on the space. A total of 50 wiki posts was analyzed adopting both quantitative and qualitative measures. The results indicated that students were most likely to use the wiki for posing their questions and disseminating solutions for peers. They also appeared highly attentive to the form of their posts in terms of grammar, spelling, and punctuation. This study makes a contribution to research on wiki-based learning.