The Effect of Vocabulary Cluster on Iranian Intermediate EFL Learners' Vocabulary Achievement

This study intended to inspect the possible effects of vocabulary cluster on Iranian Intermediate EFL learners' vocabulary achievement. It was based on the comparison between semantically and thematically –related sets to find out which type of vocabulary learning cluster was more effective on learners vocabulary learning. Sixty intermediate EFL learners were selected based on their performance on OPT test and then were randomly assigned into three groups each containing 20 subjects (one control and two experimental groups). Quasi-experimental design was used in which Pre-test and post-test were administered to collect data. The researcher employed Nations word level test as the pre-test to examine the participants' initial knowledge of common words. The experimental group (A) worked on thematic clustering, while experimental group (B) received instruction on semantic clustering and the control group received placebo. Next, all participants took part in vocabulary size test to evaluate the vocabulary achievement of the participants. The scores obtained from pre-test and post-test were analyzed through running paired sample t-test, and one-way ANOVA. The results indicated that the experimental group (B) which received semantically related sets outperformed the control group the experimental group (A) which received thematically related sets. This may have significant implications for language instructors, syllabus designers, and learners to make more advancement in vocabulary learning process through employing vocabulary cluster