The calculation and use of effect sizes—such as d for mean differences and r for correlations—has increased dramatically in second language (L2) research in the last decade. Interpretations of these effects, however, have been rare and, when present, have largely defaulted to Cohen's levels of small (d = .2, r = .1), medium (.5, .3), and large (.8, .5), which were never intended as prescriptions but rather as a general guide. As Cohen himself and many others have argued, effect sizes are best understood when interpreted within a particular discipline or domain. This article seeks to promote more informed and field‐specific interpretations of d and r by presenting a description of L2 effects from 346 primary studies and 91 meta‐analyses (N > 604,000). Results reveal that Cohen's benchmarks generally underestimate the effects obtained in L2 research. Based on our analysis, we propose a field‐specific scale for interpreting effect sizes, and we outline eight key considerations for gauging relative magnitude and practical significance in primary and secondary studies, such as theoretical maturity in the domain, the degree of experimental manipulation, and the presence of publication bias.

As a personality trait, ‘grit’ has been defined as a combination of perseverance and passion for long-term goals. Past research in social psychology has found grit as an important predictor of success across different populations in various academic and non-academic areas. Since successful mastery of a second language (L2) is highly dependent on learners’ sustained effort, the notion of grit and its relationship to language achievement gains immediate relevance in second language acquisition (SLA). The present study introduces the notion of grit and examines its relationship with motivational behaviors and language achievement in a sample of English as a foreign language learners ( n = 191). Toward these ends, a language-specific grit scale was developed and validated to measure L2 learners’ grit. L2 grit was found to be positively related to students’ language learning motivation and achievement above and beyond domain-general grit. Taken together, and consistent with results of past research in social psychology, we propose that L2 grit be considered among other more established individual differences associated with L2 development.

This article constitutes the first empirical assessment of methodological quality in second language acquisition (SLA). We surveyed a corpus of 174 studies (N = 7,951) within the tradition of research on second-language interaction, one of the longest and most influential traditions of inquiry in SLA. Each report was coded for methodological features, statistical analyses, and reporting practices associated with research quality, and the resulting data were examined both cumulatively and over time. The findings indicate not only strengths and weaknesses but a possible relationship between study quality and outcomes; improvements over time and methodological trends are also noted. In addition to providing direction for future research and research practices, the study's findings are discussed and contextualized within the research culture of SLA.Keywords effect size; interaction hypothesis; quantitative research methods; reporting practices; study quality; systematic review Progress in any of the social sciences depends on sound research methods, principled data analysis, and transparent reporting practices; the field of second Editor's Note. This systematic review article is a contribution by invitation of the new journal editor, Lourdes Ortega, and was peer reviewed by three experts.This article is based on a plenary delivered at Second Language Research Forum, 2009 (Gass) with the title Oh what a tangled web we weave and on a qualifying research paper by Plonsky (2010). We are grateful to Shawn Loewen for helpful and significant feedback on the qualifying research paper by Plonsky. Our thanks also go to Allison Dovi and Cassandra Shanbaum for their assistance with coding. All errors that remain are our own.

Research on the effects of second language strategy instruction (SI) has been extensive yet inconclusive. This meta-analysis, therefore, aims to provide a reliable, quantitative measure of the effect of SI as well as a description of the relationship between SI and the variables that moderate its effectiveness (i.e., different learning contexts, treatments, and outcome variables). A comprehensive search was conducted to collect the population of SI studies. Effect sizes were calculated for 61 primary studies, contributing a total of 95 unique samples, all of which were coded for potential moderators. The findings indicate a small to medium overall effect of SI (d = 0.49). Variables found to moderate its effectiveness include type and number of strategies, learning context (second vs. foreign language), and length of intervention. Following a contextualized interpretation of the results, the article concludes with a discussion of theoretical, practical, and methodological implications.

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