This article addresses different ways scholars conceptualize the multilingual repertoire. Formal and functional approaches investigate crosslinguistic influence across clearly demarcated languages, while dynamic systems theory and translanguaging approaches question countability and boundedness of languages. Problems with both perspectives are…

Multisite research (MSR) offers the key advantages of greater statistical power and external validity via larger and more diverse participant pools. In second language acquisition (SLA) research, recent developments in meta-analysis have created a robust foundation for MSR. Although logistical and financial obstacles can complicate expansion…

Adequate reporting of quantitative research about language learning involves careful consideration of the logic, rationale, and actions underlying both study designs and the ways in which data are analyzed. These guidelines, commissioned and vetted by the board of directors of "Language Learning," outline the basic expectations for…

Although classical statistical techniques have been a valuable tool in second language (L2) research, L2 research questions have started to grow beyond those techniques' capabilities, and indeed are often limited by them. Questions about how complex constructs relate to each other or to constituent subskills, about longitudinal development in…

Second language acquisition researchers often face particular challenges when attempting to generalize study findings to the wider learner population. For example, language learners constitute a heterogeneous group, and it is not always clear how a study's findings may generalize to other individuals who may differ in terms of language background…

This paper presents a set of guidelines for reporting on five types of quantitative data issues: (1) Descriptive statistics, (2) Effect sizes and confidence intervals, (3) Instrument reliability, (4) Visual displays of data, and (5) Raw data. Our recommendations are derived mainly from various professional sources related to L2 research but…

In this article I make the point that there has been a continuous focus on second language development in second language acquisition research for over 40 years and that there is clear empirical evidence for generalizable developmental patterns. I will both summarize some of the core assumptions of Processability Theory (PT) as an approach to…

In empirical applied linguistics research it is essential that the key variables are operationalized in a valid and reliable way, and that the scores are treated appropriately, allowing for a proper testing of the hypotheses under investigation. The current article addresses several theoretical and practical issues regarding the use of measurement…

This chapter introduces three applications of Bayesian inference to common and novel issues in second language research. After a review of the critiques of conventional hypothesis testing, our focus centers on ways Bayesian inference can be used for dealing with missing data, for testing theory-driven substantive hypotheses without a default null…

The goals of this article are to appraise second language acquisition's (SLA) disciplinary progress over the last 15 years and to reflect on transdisciplinary relevance as the field has completed 40 years of existence and moves forward into the 21st century. I first identify four trends that demonstrate vibrant disciplinary progress in SLA. I then…

This article positions research on the acquisition of pragmatics as an inquiry in the greater field of second language acquisition research. Viewing pragmatics from this intersection, I consider five areas of research that are of interest in both fields and have the potential to make significant contributions to second language pragmatics…

For decades educational psychologists have bemoaned the black box approach of much research on learning, that is, the focus on product rather than process, and the absence of fine-grained analysis of the learning process in the individual. One way that progress has been made on this point in the last couple of decades is through cognitive…

The notion of language as a complex adaptive system has been conceived within an agent-based framework, which highlights the significance of individual-level variation in the characteristics and contextual circumstances of the learner/speaker. Yet, in spite of this emphasis, currently we know relatively little about the interplay among language,…

In this article, I describe studies conducted over 25 years with secondary and post-secondary L2 learners in the United States. The evidence from these studies shows that there are important connections between students' early L1 skills and their L2 aptitude and L2 proficiency and that individual differences in students' L1 skills in elementary…

Language is a complex adaptive system: Speakers are agents who interact with each other, and their past and current interactions feed into speakers' future behavior in complex ways. In this article, we describe the social cognitive linguistic basis for this analysis of language and a mathematical model developed in collaboration between…