Past experimental studies of corrective feedback (CF) have isolated factors like grammatical complexity, learner proficiency, and L1 one by one, carefully designing experiments that eliminate the influence of “extraneous” factors. Because each factor is actually codependent, more holistic study is needed. Eleven studies, all of which had English as a Foreign Language (EFL) learners with a Persian L1 and productive measures of speech or writing, were selected for meta-analytic examination. Results suggest that type of grammatical feature, as well as associated learner variables such as L1 similarity or proficiency, collectively influence the efficacy of different CF types. As variables jointly add to the difficulty of a grammatical feature, CF providing a kind of scaffold, in the form of a written or oral reformulation from the teacher, appears to be the most effective. As grammatical difficulty decreases, learners appear to benefit from CF in which the learner is compelled to self-repair.