<![CDATA[Students’ critical reasoning ability in mathematics learning still needs improvement, especially in geometric transformation material which is considered abstract. The use of innovative technology-assisted learning models is needed to help students understand concepts more concretely. This study aimed to determine the effectiveness of the GeoGebra-assisted Problem Based Learning model in improving students’ critical reasoning ability on geometric transformation material for grade IX students of SMPN 1 Sodonghilir. This study employed a quantitative approach using a pre-experimental method with a one-group pretest-posttest design. The population consisted of all grade IX students of SMPN 1 Sodonghilir totaling 342 students, while the sample was class IX F consisting of 38 students. Data collection techniques used critical reasoning ability tests and observation sheets. Data analysis was conducted through normality testing, homogeneity testing, descriptive analysis, and paired sample t-test. The results showed that the implementation of the GeoGebra-assisted Problem Based Learning model was effective in improving students’ critical reasoning ability. The learning process became more active, interactive, and helped students understand geometric transformation concepts more easily. The findings indicate that the GeoGebra-assisted Problem Based Learning model is appropriate to be used as an alternative mathematics learning model in junior high schools. Keywords: Problem Based Learning, GeoGebra, critical reasoning ability, geometric transformation.]]>
