The combination of implicit meaning-focused input and explicit instruction has been suggested by recent research as very effective for learning L2 vocabulary; however, the time sequence for such juxtaposition has not been adequately examined through empirical studies. Therefore, this study sought to find the optimal time for combining explicit and implicit L2 vocabulary instruction using an explanatory mixed-method design. A convenience sample of 62 upper-intermediate EFL learners from three intact classes participated in this study. The Test of Academic Word List (Version A) that assesses Coxhead’s (2000) Academic Word List (AWL) was administered as a pertest. The reading book, Focus on Vocabulary 2, that has been developed based on the AWL was used for giving meaning-forced input. The target words were explicitly pre-taught in Class A (n=22), taught concurrent with encountering them in the reading text in Class B (n=20), and post-taught in Class C (n=22). Version B of the AWL Test was used as the posttest and after a 14-day retention interval (RI) as the delayed posttest. Then, 25% of the learners were orally interviewed about their attitudes toward the treatment they received. Quantitative data analysis using one-way ANCOVA revealed that explicit teaching during the reading was the optimal time and could help learners significantly do better on the immediate and delayed post-tests followed by pre-teaching. Qualitative analysis also verified the obtained quantitative results. The findings of this study imply that explicit vocabulary teaching during the reading should be practiced by EFL teachers/learners for fostering vocabulary development.
