This study investigated whether giving learners an opportunity for oral output has any positive effect on the L2 learners' acquisition of a grammatical form. Twenty-four adult ESL learners were randomly assigned to one of three groups: an output group, which engaged in a picture description task that involved input comprehension and output production; a non-output group, which engaged in a picture sequencing task that required input comprehension only; and a placebo control group. The two treatment groups were exposed to the same aural input for the same amount of time. Learning was assessed by means of a pre-test and a post-test consisting of production and reception parts. The results indicated that, contrary to our expectations, the output group failed to outperform the non-output group. On the contrary, it was the non-output group that showed greater overall gains in learning. A careful post-hoc re-examination of the treatment tasks revealed that the output task failed to engage learners in the syntactic processing that is necessary to trigger L2 learning, while the task for the non-output group appeared to promote better form-meaning mapping.