Abstrak
This study aimed to determine whether there was a significant difference in the grammar ability and vocabulary mastery of eleventh-grade students at SMAN 1 Nunukan, who were taught under the Merdeka Curriculum, and those at SMAN 2 Nunukan, who were taught using the 2013 Curriculum. Employing a causal-comparative research design, the study sampled 100 students using purposive sampling. The research instruments included the grammar and vocabulary tests which the test items were selected from listening an reading tests adopted from the TOBIC Collins test. Since the data were neither normally distributed nor homogeneous, the Mann-Whitney U Test was applied for statistical analysis. The findings revealed a significant difference in students' grammar ability between the two schools, with a p-value of 0.000. Students from SMAN 2 Nunukan, following the 2013 Curriculum, achieved a higher mean score of 93, compared to 82 for students from SMAN 1 Nunukan, who were taught using the Merdeka Curriculum. These results suggested that different teaching methods had a significant contribution to the improvement of students' grammar ability. In contrast, there was no significant difference in vocabulary mastery between students from both schools, with a p-value of 0.573. Despite the different instructional approaches, the vocabulary mastery of students in both groups remained relatively similar, with mean scores of 79 for SMAN 1 Nunukan and 76 for SMAN 2 Nunukan. This indicated that neither curriculum was notably more effective in enhancing students* vocabulary mastery. Keywords: Grammar, Vocabulary, Merdeka Curriculum, 2013 Curriculum