Using Time-Series Research Designs to Investigate the Effects of Instruction on SLA

Abstract

This paper argues that the study of second language acquisition theory and pedagogy can be enhanced through the use of time-series research designs. As quasi-experiments, time-series designs have features that improve internal validity. In addition, because these designs only require a small number of subjects, they are very practical, encouraging a greater number of empirical investigations of the many claims within the field and permitting the use of authentic measures that have high construct validity. The longitudinal nature of the designs also enhances construct validity, potentially yielding new insights into the effects of instruction on SLA. The designs utilized in two time-series studies (Kennedy, E., 1988, The Oral Interaction of Native Speakers and Non-Native Speakers in a Multicultural Preschool: A Comparison between Freeplay and Contrived NS/NSS Dyads, unpublished master's thesis, University of British Columbia, Vancouver; Mellow, J. D., 1996, April, A Longitudinal Study of the Effects of Instruction on the Development of Article Use by Adult Japanese ESL Learners, unpublished manuscript, University of British Columbia, Vancouver) are reviewed in order to illustrate the design features, the questions that may be investigated, and the issues that are raised in interpreting data.

Effectiveness of L2 Instruction: A Research Synthesis and Quantitative Meta‐analysis

“…First, testing of learning outcomes usually favors explicit treatments by asking learners to engage in explicit memory tasks and/or in discrete, decontextualized L2 use. In addition, explicit treatments are typically more intense and varied than implicit treatments, and implicit treatments may require longer post-intervention observation periods for nonlinear learning curves to be detected (see also Mellow, Reeder, & Forster, 1996). Second, the essential features that supposedly distinguish FonF and FonFS instructional approaches have been inconsistently operationalized, and the wide range of actual observed effect sizes within each category suggests that the particular subtypes of instruction need to be further investigated in their own right by means of careful replication.…”

Does Type of Instruction Make a Difference? Substantive Findings From a Meta‐analytic Review

“…First, testing of learning outcomes usually favors explicit treatments by asking learners to engage in explicit memory tasks, discrete, decontextualized L2 use or both. In addition, explicit treatments are typically more intense and varied than implicit treatments, and implicit treatments may require longer post-intervention observation periods for nonlinear learning curves to be detected (see also Mellow, Reeder, & Forster, 1996). Second, the essential features that supposedly distinguish FonF and FonFS instructional approaches have been inconsistently operationalized, and the wide range of actual observed effect sizes within each category suggests that the particular subtypes of instruction need to be further investigated in their own right by means of careful replication of experimental variables.…”

Effects of Recasts on the Acquisition of the Aspectual Form ‐te i‐(ru) by Learners of Japanese as a Foreign Language

“…This study employed a time-series design (Mellow, Reeder, & Forster, 1996) involving four case studies in concurrent replication.…”