Abstrak
This study aims to improve students' vocabulary mastery through the application of metalanguage instruction with a focus on introducing parts of speech, including nouns, verbs, adjectives, and adverbs in narrative texts. This study was conducted at MTs Negeri Tarakan with 31 students in class VIII-A as the research subjects. The method used was Classroom Action Research (CAR) using the Kemmis and McTaggart (2014) model, which consists of four stages: planning, acting, observing, and reflecting. The research was conducted in two cycles, each consisting of three meetings. The research instruments used were a vocabulary test to measure students' vocabulary mastery and an observation sheet for teacher and student activities. The results showed an increase in students' vocabulary mastery from cycle I to cycle II. In cycle I, the results of the students' vocabulary test did not meet the success criteria, as only 39% of students achieved a score of ≥70, per the Learning Objective Achievement Criteria (KKTP). However, in cycle II, the classical mastery rate increased to 77% of students achieving the KKTP, thus fulfilling the research success criteria. In addition, the observation results showed an increase in teacher and student activity in each meeting, with students more active in participating in discussions, identifying vocabulary, and classifying it by word class. Based on the data processing results, it can be concluded that the application of metalanguage instruction is effective in improving eighth-grade students' vocabulary mastery at MTs Negeri Tarakan.