Online collaborative writing tasks are frequently undertaken in forums and wikis. Variation between these two communication modes has yet to be examined, particularly type of feedback and its effects. We investigated the type of feedback and the impact of English native-speakers' feedback on Spanish peers' discourse restructuring in the context of an online collaborative writing task involving tertiary level students of English and Spanish as foreign languages. The collaborative task was to develop a tourist brochure in the foreign language in a Moodle e-learning environment. Two corpora were compiled of learner exchanges. The communication formats of both forums and wikis determined the type of feedback provided by peers in online communication tasks. Regarding the effect of such feedback, we can conclude that, although morphosyntactic and lexical feedback is largely acknowledged and incorporated, the Spanish peers seemed to accept it without further follow-up or discussion. Affective feedback, in the main, provoked no language-based reaction. These effects vary, however, by forums and the wiki sub-tasks. (Contains 3 figures, 11 tables, and 3 notes.)