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

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and Non-Native Speakers in a Multicultural Preschool: A Comparison between Freeplay and Contrived NS/NSS Dyads, unpublished master's thesis, University of British Columbia, Vancouver; Mellow, J. D., 1996, April, A Longitudinal Study of the Effects of Instruction on the Development of Article Use by Adult Japanese ESL Learners, unpublished manuscript, University of British Columbia, Vancouver) are reviewed in order to illustrate the design features, the questions that may be investigated, and the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.