This study was motivated by Skehan's (1996, 1998) hypothesis about the potential of post-task anticipation to direct learners' attention towards form and previous online L2 collaborative writing research that found prioritization of meaning in this context. It investigated the effects of post-task anticipation on text length, accuracy and complexity, and learners' perceived effects of anticipation, in online collaborative writing. Ninety-eight Thai EFL learners of English on an online university course were divided into control and experimental groups. The control group performed the main online collaborative writing task without foreknowledge of a post-task, while the experimental group anticipated a peer language evaluation post-task. Texts written during the main task and questionnaire responses were assessed. Overall, statistical analyses revealed that post-task anticipation did not lead to increased attention to form. Independent-sample t-tests did not detect significant effects of post-task anticipation on text length or accuracy, and significantly more complex language was observed in the control group. Possible reasons for these findings are discussed. Despite the lack of positive outcomes for performance, questionnaire responses indicated that post-task anticipation might promote engagement during the main task.