The study compares the effectiveness of Processing Instruction (PI) and meaningful Production-Based Instruction (PB) on the acquisition of gender agreement in Greek as a second language (L2). Both methods emphasize focusing on form and meaning in parallel. However, PI employs only input activities, whereas output is considered crucial for PB. Sixteen elementary-school students, beginner learners of Greek as an L2, divided into two groups, participated in the study. One group received PI and the other PB, while both groups also underwent brief explicit instruction, albeit at different stages of the teaching interventions. The relative effectiveness of the two methods was measured by means of a comprehension task and a production task, administered before and after the teaching interventions. Results indicate that both groups improved in the production task, corroborating previous research. In the comprehension task, however, there was statistically significant improvement only for the PB group. This finding is interpreted as an indication that the PB group was able to better exploit morpho-phonological cues to gender. It is not clear however whether this superior effect for the PB group should be attributed to the output activities per se or the timing of the explicit instruction.