VietTESOL International Convention 2026

This study investigated whether form-focused instruction within a Task-Based Language Teaching (TBLT) framework enhances acquisition of the English third-person singular -s beyond task engagement alone. While TBLT has been widely advocated for communicative language teaching, debates persist over whether and how explicit grammar instruction should be integrated, particularly regarding its differential effects on implicit versus explicit knowledge systems. Ninety-eight Vietnamese EFL learners were assigned to three conditions: a task-only control group, a task-plus-inductive instruction group, and a task-plus-deductive instruction group. Explicit knowledge was measured using a Grammaticality Judgment Test (GJT), while implicit processing sensitivity was assessed through a self-paced reading (SPR) task. Both measures were administered at pretest and posttest. Mixed-effects model analyses revealed that all three groups demonstrated significant pre-to-post improvement overall. On the GJT, no reliable group differences emerged in gain scores, suggesting that task engagement alone was sufficient for explicit knowledge development regardless of instruction type. However, SPR analyses revealed that both instructed groups exhibited significantly greater reading time disruption on ungrammatical sentences at the spillover regions at posttest compared to the control group, indicating deeper implicit sensitivity to morphosyntactic violations. These findings suggest a partial dissociation between explicit and implicit learning outcomes under different TBLT conditions, and support a weak interface position whereby explicit instruction may facilitate implicit processing without producing measurable advantages on declarative knowledge measures. Pedagogical implications for grammar instruction within TBLT contexts are discussed.