Abstrak
Vocabulary plays an important role in mastering English, yet many seventh-grade students at UPTD SMPN 3 Kec. Harau faced difficulties in understanding word forms, grasping meanings, and applying vocabulary in context, partly because the teacher used conventional methods without content-language integration. To overcome this problem, the researcher used CLIL-based guided practice (Content and Language Integrated Learning) which integrates content and language through meaningful, contextually relevant materials and structured, scaffolded activities that engage students more actively and facilitate deeper vocabulary processing. This study aimed to determine the effectiveness of using CLIL-based guided practice to improve students' vocabulary mastery in learning English. A quantitative quasi-experimental design was employed, involving an experimental class (VII.1, n=29) that received structured CLIL-based guided practice through procedural texts about Indonesian snacks, and a control class (VII.2, n=28) taught using traditional, teacher-centered methods without explicit content-language integration. Data were collected via pre-tests and post-tests consisting of multiple-choice and matching items, which were validated and tested for reliability. Statistical analyses included normality and homogeneity tests, paired sample t-tests, and independent sample t-tests using SPSS. The findings reveal significant differences in vocabulary mastery both within and between the two groups. The experimental group's mean score increased substantially from 57.07 on the pre-test to 77.24 on the post-test, a gain of 20.17 points (p = 0.000), confirming a significant positive effect of CLIL-based guided practice. The control group also showed improvement, with a mean score rising from 55.89 to 61.25, a gain of only 5.36 points (p = 0.000). Although both groups demonstrated statistically significant gains, the experimental group's improvement was nearly four times larger. More importantly, the independent t-test revealed a significant post-test difference between the groups, with a mean difference of 15.991 (p = 0.000), indicating that the experimental group outperformed the control group by approximately 16 points on average. These results demonstrate that CLIL-based guided practice is substantially more effective than conventional instruction in enhancing vocabulary across the dimensions of form, meaning, and usage.