<![CDATA[This study aimed to determine the validity, practicality, and effectiveness of a Student Worksheet based on Project-Based Learning (PjBL) integrated with Batak Toba ethnoscience to improve students’ critical thinking skills in the topic of elements, compounds, and mixtures among eighth-grade students at SMP Negeri 8 Medan in the 2025/2026 academic year. This study employed a research and development (R&D) method using the ADDIE model, which consists of five stages: Analysis, Design, Development, Implementation, and Evaluation. Data were analyzed using Aiken’s V index, the Independent Samples t-test, N-Gain, and effect size. The results showed that the developed student worksheet met the criteria for very high validity in terms of content, learning, and design. The practicality assessment indicated that the worksheet was highly practical, with a teacher response rate of 98.53%, a student response rate of 91.15% in the small-group trial, and 90.56% in the large-group trial. The effectiveness test revealed a statistically significant difference between the experimental and control classes based on the Independent Samples t-test, with a significance value (two-tailed) of p < 0.001. The experimental class achieved an N-Gain score of 0.8674, which falls into the high category, while the control class obtained a score of 0.6807, which falls into the moderate category. Furthermore, the effect size value of 1.162521 indicated a strong effect of the developed worksheet. Based on these findings, it can be concluded that the developed PjBL-based student worksheet integrated with Batak Toba ethnoscience meets the criteria for very high validity, high practicality, and effectiveness in improving students’ critical thinking skills in the topic of elements, compounds, and mixtures among eighth-grade students at SMP Negeri 8 Medan. Keywords: Student Worksheets; Project Based Learning (Pjbl); Batak Toba Ethnoscience; Critical Thinking Skills.]]>
