This paper reports on a study investigating the role of working memory in predicting L2 development under immediate and delayed corrective feedback (CF) conditions. A total of 106 seventh-grade EFL learners were assigned to three groups: Immediate CF, Delayed CF, and Task Only. Each group underwent three treatment sessions during which they performed six focused communicative tasks – two in each session – involving the use of the English past tense. The Immediate CF group received feedback on their erroneous use of the target structure during their task performance in Session 1; the Delayed CF group did not receive feedback until the final treatment session; and the Task Only group performed the communicative tasks without receiving any feedback. Treatment effects were measured through a grammaticality judgement test and an elicited imitation test. Working memory was measured by means of an operation span test. The results revealed that working memory was a significant predictor only of the effects of delayed CF, not those of immediate CF or Task Only. The findings suggest that delayed CF may have imposed a heavier processing burden on the learners’ working memory due to the need to match the delayed feedback with the errors in their procedural knowledge manifested in previous sessions. Based on the results of this and other empirical studies, the authors argue for the superiority of immediate feedback over delayed feedback.