<![CDATA[Vocabulary mastery is a fundamental component of English language learning and plays a crucial role in determining learners’ overall language proficiency. Adequate vocabulary knowledge enables students to comprehend texts, express ideas, and communicate effectively across the four language skills. However, empirical studies indicate that vocabulary mastery among first-grade senior high school students in Indonesia remains relatively low, largely due to the continued reliance on conventional, textbook-centered teaching methods that often lead to low engagement and limited retention. Previous research has highlighted the potential of game-based learning to enhance vocabulary acquisition, yet studies employing a quasi-experimental design at the first-grade senior high school level remain limited. Therefore, this study aimed to investigate the effectiveness of using Blooket as a game-based learning medium in improving first-grade senior high school students’ vocabulary mastery. This study employed a quantitative approach using a quasi-experimental design involving an experimental group and a control group. The participants consisted of 66 first-grade senior high school students selected through cluster random sampling. Data were collected using vocabulary pre-tests and post-tests and analyzed using descriptive statistics, the Mann–Whitney U test, and effect-size analysis. The findings revealed a statistically significant difference in post-test scores between the experimental and control groups, with students taught using Blooket achieving higher vocabulary mastery. The effect-size analysis indicated a moderate effect, suggesting that Blooket provided meaningful educational benefits beyond traditional instruction. In conclusion, Blooket is an effective game-based learning medium that enhances students’ vocabulary mastery, engagement, and motivation. Its integration into English vocabulary instruction is recommended as a practical alternative to conventional teaching methods in senior high school EFL contexts.]]>
