The Presentation-Comprehension-Practice-Production (PCPP) approach is often used in Japanese junior high school English classes, with a focus on communicative interaction. Although ample communicative activities are implemented in a PCPP approach, teachers are likely to present grammar and vocabulary in the comprehension stage using a traditional teacher-centered deductive method. In this study, Data-Driven Learning (DDL) was implemented as a means to Focus on Form in a PCPP approach and students explored language data to understand vocabulary and grammar in a learner-centered way. To investigate the effectiveness of this DDL method, we implemented deductive (traditional) and inductive (DDL) instruction at two schools. In School A, DDL was used to review and deepen known vocabulary, and at School B, to learn new grammatical items. Accordingly, four groups totaling 121 students took part in the research. Results show that DDL was as effective as traditional instruction in a posttest given one week after instruction. However, after four weeks, the DDL groups retained the gained knowledge better than the traditional groups at both School A and B. Furthermore DDL students performed a more detailed analysis on finding grammar rules in the posttests. Therefore, we can conclude that the use of DDL was effective for retaining language knowledge and for developing students’ ability to explore language rules.
