This chapter reports on a classroom-based quasi-experimental study by focusing on its methodological aspects. The study's objectives were twofold: (1) to examine the effect of metacognitive instruction (MI) in which learners were instructed about the benefits of receiving corrective feedback (CF), and (2) to compare the effects of two CF types - input-providing vs. output-prompting CF. Eighty-three EFL learners from four intact classes at a private university in Chile were assigned to one of four conditions: MI plus input-providing CF, input-providing CF only, MI plus output-prompting CF, and output-prompting CF only. The results showed that MI helped learners benefit from CF. Focusing on the ecological validity, we argue that providing learners with interventions that were seamlessly deployed in genuine classroom contexts permitted the examination of authentic classroom instruction with minimal disturbance, thereby allowing the observation of the effects of MI and CF without the potentially confounding variables of researcher intrusion and unfamiliar data collection context.