The effects of deliberately and selectively manipulating instructional conditions are at the heart of instructed second language acquisition (ISLA) research and, ideally, are designed to inform practice. Knowing how an intervention works, by what mechanisms and processes the treatment is beneficial—and for whom—are complex questions. In this piece, we problematize intervention-based research paradigms that do not account for context, individuals and their proactivity, or temporal variation. We highlight several key challenges that remain for ISLA research and propose a more reflexive approach to intervention that attends to these central considerations in implementing study designs.
