This study aimed to examine changes in students’ learning outcomes and assess the perceived effectiveness and practicality of PhET media in learning about states of matter and their changes among seventh-grade students at SMPN 2 Watubangga. A quantitative descriptive approach using a One-Group Pretest-Posttest Design was employed. The participants were 20 seventh-grade students in the 2026/2027 academic year. PhET-supported learning activities were implemented during the study period from July 13 to August 3, 2026. Data were collected using a 15-item objective test of learning outcomes and a questionnaire consisting of 32 statements to assess the effectiveness and practicality of the medium. Learning gains were analyzed using the normalized gain (N-Gain), while questionnaire responses were analyzed descriptively using percentages. The mean learning outcome score increased from 58.25 on the pretest to 83.75 on the posttest, while the proportion of students achieving learning mastery increased from 25% to 100%. The mean N-Gain was 0.6008 (60.08%), indicating a moderate level of learning improvement. Separately, questionnaire results yielded an effectiveness score of 84.01% and a practicality score of 83.37%, both categorized as very high. These percentages represent respondents’ assessments of the learning medium and are distinct from the N-Gain, which measures improvement in learning outcomes. Overall, the findings indicate that the use of PhET media was associated with improved learning outcomes and was positively perceived by students in the context of this study. However, because the study employed a one-group design without a comparison group, the findings do not establish that PhET media is more effective than other instructional approaches