Despite the burgeoning research on exploring learner engagement with feedback, how second language (L2) learners’ engagement with feedback in different processing conditions influences their subsequent writing development is under-explored. This study examines the effects of individual and collaborative processing (languaging) of teacher feedback on Chinese lower-secondary school EFL learners’ writing development. Eighty-one students aged 13–14 with A1-A2 levels of English proficiency (according to the Common European Framework of Reference) from two classes and two experienced English teachers participated in the study. Students were provided with comprehensive teacher feedback and were asked to process feedback provided on three writing tasks through either individual written or collaborative oral languaging over six weeks. Pre-, post-, and delayed post-tests were administered. Students’ writing development was analysed using complexity, accuracy, and fluency measures, as well as content and organisation writing scores. Findings showed that the two conditions did not influence students’ writing complexity and fluency differently, while only the collaborative oral languaging condition contributed to students’ sustainable accuracy gains. Results based on the analytic writing scores suggested that students in the two conditions significantly improved content and organisation scores over time. Pedagogical and research implications regarding implementing the two feedback processing conditions are discussed.