This meta-analysis offers a snapshot of thirty-five years (1980–2015) of research on instructed second language acquisition (ISLA). Fifty-four empirical studies involving a total of 5,051 second language learners – sampled from six applied linguistics journals, Applied Linguistics, Language Learning, Language Teaching Research, The Modern Language Journal, Studies in Second Language Acquisition, and TESOL Quarterly – were aggregated for the effects of second language (L2) instruction, yielding an overall large effect size, g = 1.06, 95 % CI = 0.84−1.29. Data were further analysed to identify factors that can modulate the efficacy of instruction. While a minor difference was detected between explicit and implicit instruction, statistically significant effects were found for modes of outcome measures, learners’ onset L2 proficiency, research settings, and intensity of instruction.

The current study is an approximate replication of Gray and DiLoreto’s (2016) study, which proposed a model predicting that course structure, learner interaction and instructor presence would influence students’ perceived learning and satisfaction in online learning, with student engagement acting as a mediator between two of the predictors and the outcome variables. Using mixed methods, the current study investigated whether Gray and DiLoreto’s model would be able to explain the relationships among the same variables in a computer-assisted language learning environment. A mediation analysis was conducted using survey responses from a sample of 215 college-level students, and qualitative analysis was conducted on the survey responses from a subsample of 50 students. Similar to Gray and DiLoreto’s study, positive correlational relationships emerged between the variables. However, the model proposed by Gray and DiLoreto did not fit our data well, leading us to suggest alternative path-analytic models with both student engagement and learner interaction as mediators. These models showed that the role of course organization and instructor presence were pivotal in explaining the variation in students’ perceived learning and satisfaction both directly and indirectly via student engagement and learner interaction. Moreover, qualitative analysis of students’ responses to open-ended questions suggested that from students’ perspectives, course structure was the most salient factor affecting their experiences within online language learning contexts, followed by learner interaction, and then by instructor presence.

This article offers a methodological synthesis spanning 35 years of instructed second language acquisition research on the efficacy of form-focused instruction. Eighty-eight (quasi-) experimental studies were sampled from six academic journals: Applied Linguistics, Language Learning, Language Teaching Research, Modern Language Journal, Studies in Second Language Acquisition, and TESOL Quarterly. The focus of analysis was on five sets of variables: (1) research design, (2) participants, (3) context in which the studies were conducted, (4) instructional treatment, and (5) outcome measures. Results revealed that since Norris and Ortega’s (2000) seminal study, the research domain has grown, not only with respect to the number of studies published, but also with regard to the addition of previously unexamined L1 groups, increase in the number of studies investigating implicit instruction, greater use of multiple measures of learning, and more pretesting and delayed posttesting. However, a number of methodological weaknesses have also persisted.

Complex Dynamic Systems Theory (CDST), an instantiation in applied linguistics of complexity epistemology that transcends disciplinary boundaries, has gained much traction and momentum over the last decade, finding expressions in a fast-growing number of empirical second language developmental studies. However, the literature, while rapidly expanding, has displayed much confusion, notably oscillating between invoking CDST as a metatheory and as an object theory. Then, too, the metaphorical genesis of CDST—the metaphorical adoption of complexity epistemology from physical sciences—has seemed to invite miscellaneous interpretations, rendering CDST an ostensibly all-in-one conceptual prism. This article explores the epistemology of CDST, tracing its ontology and examining its role in second language developmental research. This enables a more nuanced understanding of CDST, while at once surfacing critical issues and directions for future research, as it moves toward a pluralistic approach to investigating CDST as a potentially unique lens on second language development.

Vocabulary development is indisputably a vital aspect of second language acquisition. In spite of the abundant attention it has garnered over the past few decades, it remains unclear how adult learners fare with intentional and incidental ways of learning. The current study investigated the effects of intentional learning (via studying a word list), incidental learning (via reading), and combined intentional-andincidental learning (via studying a word list followed by reading) conditions on 30 adult learners’ second language vocabulary acquisition. Vocabulary acquisition was measured in terms of percentage gains as well as changes in the depth of vocabulary knowledge. Results showed that while both the intentional and incidental modes of learning led to vocabulary gains, the combined intentional-and-incidental condition resulted in significantly greater gains than either the intentional-only or the incidentalonly condition. No significant differences were found between the incidental-only and intentional-only conditions.