Task Complexity and Metacognitive Knowledge in EFL Grammar Learning: A Critical Review and Research Agenda

This review critically examines the relationship between task complexity and metacognitive knowledge in English as a Foreign Language (EFL) grammar learning. Synthesizing available empirical and conceptual research (2010–2025), the analysis reveals that while task complexity and metacognitive knowledge have each been independently investigated in relation to grammar learning outcomes, only one empirical study has directly examined their interaction. Evidence indicates that tasks with higher involvement load enhance morphosyntactic accuracy, and metacognitive strategies, particularly planning, monitoring, and evaluation, predict grammar learning success. However, the field lacks integrated research examining how these two dimensions interact. This review identifies this gap, synthesizes findings from separate research strands, proposes a conceptual model for understanding their potential interaction, and outlines a research agenda for future investigation. The review concludes that understanding how task complexity and metacognitive knowledge jointly influence grammar learning represents a critical direction for future research.