This article reports on a study exploring the differential effects of immediate and delayed corrective feedback (CF) on the acquisition of the English past tense. One hundred and forty-five seventh-grade EFL learners were assigned to four groups: Immediate CF, Delayed CF, Task Only, and Control. Each experimental group performed six focused communicative tasks, two each in three treatment sessions, eliciting the use of the English past tense. The Immediate CF group received feedback on their erroneous use of the target structure in the first session, the Delayed CF group received feedback in the final session, and the Task Only group performed the communicative tasks without receiving any feedback. The Control group only took the achievement tests. The effects of the feedback treatments were measured through an untimed grammaticality judgment test and an elicited imitation test. Mixed-effects analyses examining the influence of both fixed and random factors demonstrated that immediate CF was more facilitative of L2 development than delayed CF. The results suggest the importance of addressing linguistic errors before they are proceduralized in the interlanguage.