<![CDATA[This study aimed to determine the effectiveness of content mastery services in reducing verbal aggressiveness among eleventh-grade students at SMA Negeri 4 Jambi City. Verbal aggressiveness is a serious problem in schools that negatively affects students’ psychological conditions and the learning environment. This study used a quantitative approach with a quasi-experimental design employing a nonequivalent control group design. The population consisted of 432 students, while the sample involved 30 students selected through purposive sampling, consisting of 15 students in the experimental group and 15 students in the control group. Data were collected using a verbal aggressiveness questionnaire and analyzed using normality tests, homogeneity tests, paired sample t-tests, independent sample t-tests, and Cohen’s d effect size test with the assistance of SPSS. The results showed a decrease in students’ verbal aggressiveness after receiving content mastery services, with the average pretest score decreasing from 36.60 to 29.53 in the posttest. The paired sample t-test showed a significance value of 0.002 < 0.05, indicating that content mastery services were effective in reducing students’ verbal aggressiveness. The Cohen’s d value of 1.010 indicated a large effect size.]]>
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