Consciousness-raising (CR) task is a new way of teaching grammar developed in communicative contexts although little has been written on the effectiveness of CR tasks in EFL setting. The present study is an attempt to investigate the impact of CR tasks in Iranian EFL setting by comparing them with deductive, grammar lessons common in the Iranian schools. The subjects of this study were 80 EFL pre-university male students who were randomly assigned to an experimental group and a control one. The control group received three ordinary teacher-fronted, deductive lessons, a common way of teaching methodology in Iran, on three grammatical structures (adverb placement, indirect object placement and the use of relative clause). The experimental group, however, was treated with three ‘consciousness-raising’ (CR) tasks dealing with the same target structures. The results showed that in the short-run, CR tasks were as effective as deductive approach in promoting the learners’ grammatical knowledge while in the long-run, the CR group maintained their gains more effectively than the deductive group. The conclusion is that CR tasks can function more effectively than deductive approach if the following conditions are met: (a) performing the consciousness-raising tasks in learners’ L1; (b) providing the learners with feedback whenever they encounter a problem in solving the tasks; (c) grouping the learners in such a way that at least one learner in each group would be more proficient than the other members to help the less proficient ones understand and discover the rules more effectively.