This study explores the development of Geogebra-based mathematics instructional media and its impact on the critical thinking skills of cleventh-grade high school students in the topic of geometric transformations. The development
process followed the ADDIE model, which includes needs analysis, instructional design based on the Indonesian Realistic Mathematics Education (PMRI) approach,
media development, classroom implementation, and evaluation. The resulting product consists of four interactive menus and was validated by content and media
experts, yielding validity scores of 95% for the media and 85% for the content, indicating strong feasibility. A limited trial conducted in class received highly
positive student responses, with a practicality score of 85%. Effectiveness was determined to be moderate, with an N-gain score of 56%. Statistical analysis using the paired sample t-test produced a significance value of 0.000, indicating a significant improvement in students' critical thinking skills after using the media. These findings confirm that the developed Geogebra-based instructional media is
valid, practical, and effective in enhancing high-level cognitive skills and can be widely applied to support engaging and conceptually rich mathematics learning.