The Effects of Derivational Suffixes on English Vocabulary Knowledge in Thai High School Learners

Abstract

Although derivatives are an essential component of a morphological word and cornerstones for vocabulary knowledge, L2 vocabulary research has shown that EFL learners still have inadequate vocabulary knowledge. Therefore, this study attempted to investigate the effect of derivational suffix instruction on vocabulary knowledge. Fifty-eight high school learners were recruited to participate in the study. The learners were divided into two groups: control (n=29) and experimental (n= 29). The experimental group received a regular English course with an emphasis on derivational suffix instruction, whereas the control group only received a regular English course. Two tests of receptive and productive derivational suffixes were developed and piloted to measure high school learners’ suffix knowledge. Questionnaire was also administered to explore the experimental participants’ perceptions of derivational suffix instruction in facilitating vocabulary knowledge. Descriptive and inferential statistics, including pair-sample t-tests and independent-sample t-tests, were conducted to analyze the quantitative data. The results showed that high school learners in both groups significantly performed better on the posttest than on the pretest. The results analysis also revealed that experimental learners significantly outperformed their control counterparts. These findings suggest the efficacy of derivational suffix instruction on English vocabulary knowledge in Thai high school learners. In addition, the questionnaire analysis indicated that experimental high school learners had a positive perception of derivational suffix instruction in improving their vocabulary knowledge. Together, the current findings highlight the importance of derivational suffixes in vocabulary acquisition and development. The study also points out the implications for practitioners and researchers. Other relevant implications and suggestions for future studies are also addressed.

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