The Importance of Teaching Prepositional Idioms Through Explicit Vocabulary Instruction and Interactive Activities to Develop the English Language Skills of Matthayom 3 (Grade 9) Students of the Demonstration School of Suan Sunandha Rajabhat University (A Classroom Action Research)

Abstract

Vocabulary learning is a fundamental component of second language acquisition, as effective communication cannot occur without sufficient lexical knowledge. This classroom action research examined the effectiveness of explicit vocabulary instruction combined with interactive and contextualized activities in teaching English prepositional idioms to third-year middle school students (Grade 9/Matthayom 3). Grounded in theories of direct instruction, vocabulary acquisition, interactional hypothesis, and intrinsic motivation, the study employed a Plan–Act–Observe–Reflect (P-A-O-R) action research cycle. The participants consisted of 94 students aged 14-16 years during the second term. Instructional strategies included the use of authentic comic strips, guessing meaning from context, vocabulary matching games, cooperative learning activities, dialogue construction, and realia. Data were collected through classroom observations, students’ oral and written outputs, and participation in learning activities. The findings indicated that students demonstrated improved comprehension, retention, and the appropriate use of prepositional idioms in both spoken and written communication. The study concludes that integrating explicit vocabulary instruction with interactive, game-based, and contextualized strategies effectively enhances vocabulary acquisition and communicative competence among secondary-level English language learners.