A meta-analysis of graduate research on teaching strategies used for improving Thai students’ English skills

This is study aimed to 1) analyze the characteristics of graduate research on teaching strategies used for improving the English skills of Thai students; 2) evaluate the quality of the aforementioned graduate research, and 3) compare the characteristics of the graduate research to the standard index. A total of 22 experimental graduate research reports written at one public Thai university in English and published in 2004-2020 were synthesized. The research design was quantitative. The research instruments were a recording form and an evaluation form. The data were analyzed using descriptive statistics, t-test, and one-way ANOVA. The results showed that graduate research mostly focused on vocabulary (31.81%). The types of strategy were used the most was teaching materials (72.72%). Secondary school was the highest levels of students’ education in the research (63.63%). Eighteen studies had a total score at a very high level, and four studies had a total score at a high level. The sample size had a significant effect on effect size at the level of .05, whereas the sampling technique affected effect size at the statistically significant level of .01. Thus, the difference in these variables affected the difference in learning achievement. The meta-analysis found that the sample size variable with the highest mean effect size was 30-39 students, with an average effect size of 3.23. Teaching in a classroom of 30-39 students will therefore lead to better academic achievement than other room sizes. For sampling technique, convenience sampling had the highest mean effect size at 3.02, followed by simple random sampling at 1.39 and purposive sampling at 1.33.