Recently, there has been a shift in the perception of tasks. Tasks are no longer viewed as 'one-off' activities, and the importance of studying the role of task repetition has been increasingly addressed (Bygate, 2018). However, the way task repetition effects are mediated by other instructional conditions such as corrective feedback has not been widely researched. The current study examined the effects of task repetition and indirect synchronous written corrective feedback (WCF) during collaborative writing on the quality of students' written task performance and the learning of Korean grammar. Fifty-four Korean as a foreign language learners completed a pretest, two collaborative writing tasks, and two posttests over 10 weeks. Their task performance was analysed in terms of complexity, accuracy and fluency, and the pretest and posttest results were scored for both suppliance and accuracy of the production of target grammatical features. The findings showed that task repetition improved writing fluency, and while synchronous WCF negatively impacted fluency during collaborative writing, it facilitated accuracy in students' writing. In terms of the learning of target grammatical features, no significant benefit of synchronous WCF was found.