This article reports a study examining the impact of pre-task explicit instruction on L2 learning outcomes. 72 eighth-grade EFL learners at a Chinese middle school were assigned to three groups: Explicit Instruction + Task (EI), Task Only, and Control. Both experimental groups performed two communicative tasks providing opportunities for the learners’ exposure to and use of the English passive voice―the target structure. The EI group were given a brief grammar lesson on the target structure before performing the tasks, while the Task Only group performed the tasks without receiving the grammar lesson. The control group did not receive any instructional treatment. Learning was measured via an untimed grammaticality judgement test and an elicited imitation test. The results showed that pretask instruction resulted in greater learning gains, but the effects were only evident on the grammaticality judgment test. The results suggest that pretask instruction may facilitate the learning of explicit knowledge but its effects on implicit knowledge remain unclear.