Although many researchers have worked on the role of feedback in immersion programs on second language learners' production, still little is known about the role of different types of immediate feedback on the grammatical accuracy of learners' production. When, where and with who different types of immediate feedback such as prompts and recasts and their different subcategories might be appropriate? The purpose of the present research was to know which types of immediate oral feedback could better help Iranian EFL learners to produce the correct form of the tense markers of their target language--English. One of the primary objectives of the present study was to examine the effects of two types of oral feedback--namely explicit correction and implicit or-choice feedback--on Iranian EFL learners' production of different tense markers in English. The results were in favor of explicit correction over implicit or-choice feedback in helping learners to produce correct grammatical tense markers.