Half a century has passed since the emergence of the concepts of error and interlanguage as a paradigm shift for reconsidering and analyzing issues related to second language acquisition and foreign language learning. This review paper aims to provide a comprehensive overview of SLA research outcomes that can aid teacher educators and in-service teachers in further advancing their understanding of the field of SLA and teacher education. This paper commences by defining second language acquisition (SLA), instructed second language acquisition (ISLA), and foreign language learning. It then examines 34 review articles and comprehensive books on SLA published between 1967 and 2022 and scrutinizes the historical and thematic developments that have shaped the field. Furthermore, the article summarizes current issues related to SLA research and L2 instruction and conducts a critical assessment of recent studies conducted in EFL settings. The review emphasizes the need for greater teacher awareness of research areas such as pronunciation, vocabulary, pragmatics, writing, and learner engagement. The results also suggest educational implications for implementing ISLA in classroom practice in Japan, such as re-affirming the nature of the EFL environment, implementing pragmatics instruction, and fostering learners’ engagement. Finally, this article concludes that future studies should adopt interdisciplinary and longitudinal designs to strengthen the link between SLA and teaching English and teacher education studies and promote teachers’ expertise in incorporating research findings related to the L2 acquisition process in foreign language classroom practice.

A growing number of studies have addressed the issue concerning the use of ‘because-clauses’ as sentence fragments by Japanese learners of English. The purpose of the present study is to investigate and analyze the misuse of ‘because-clauses’ by Japanese English learners and to explore pedagogical implications. Sixty-one Japanese senior high school students participated in the study. The research examined L2 learners’ production and comprehension of because-clauses and interview responses. The results revealed that more than half of the L2 learners employ ‘because-clauses’ as sentence fragments in their writing and that over 90% of them accept the usage as correct in their grammatical judgment test. The results from interviews with the L2 learners also indicated that there is a possibility that their first language has an influence on the misuse of ‘because-clauses’. The study concludes with pedagogical implications and recommendations for future research.