<![CDATA[Critical thinking skills are skills that students must have in learning mathematics. Initial observations showed that students still had difficulty in understanding the concept of solving fraction problems. The cause was learning that was still conventional and did not involve students actively. This study aims to determine the effectiveness of the Problem Based Learning learning model on critical thinking skills in mathematics lessons. This study used a quantitative approach with a quasi-experimental design (Nonequivalent Control Group Design). The sample consisted of 42 students, namely the experimental class and the control class. The research instrument was a critical thinking ability test in the form of essay questions, which were given before and after treatment. In addition, observations were made to measure the implementation of the PBL model during the learning process. The results showed that the PBL model was effective in students' critical thinking skills. The average pre-test score in the experimental class was 60, while the control class was 62.5. After being given treatment, the post-test score of the experimental class became 85.4, while the control class was 74.2. The results of the sample t-test showed a significance value of 0.001 (p <0.05), there was a significant difference between the two groups. The n-gain test value reached 59.70%, which means that the PBL model on students' critical thinking is quite effective compared to the conventional model which is only 45.55%, which means it is less effective to apply. This model can be an alternative to innovative learning that is interactive and student-centered, so it is recommended to be applied in mathematics learning in elementary schools. ABSTRAKKemampuan berpikir kritis merupakan keterampilan harus dimiliki siswa dalam pembelajaran matematika. Observasi awal menunjukkan bahwa siswa masih mengalami kesulitan dalam memahami konsep menyelesaikan soal pecahan. Penyebabnya adalah pembelajaran yang masih bersifat konvensional dan kurang melibatkan siswa secara aktif. Penelitian ini bertujuan untuk mengetahui efektivitas model pembelajaran Problem Based Learning pada kemampuan berpikir kritis pada pelajaran matematika. Penelitian ini menggunakan pendekatan kuantitatif dengan desain kuasi eksperimen (Nonequivalent Control Group Design). Sampel terdiri dari 42 siswa, yaitu kelas eksperimen dan kelas kontrol. Instrumen penelitian berupa tes kemampuan berpikir kritis dalam bentuk soal esai, yang diberikan sebelum dan sesudah perlakuan. Selain itu, observasi dilakukan untuk mengukur keterlaksanaan model PBL selama proses pembelajaran. Hasil penelitian menunjukkan bahwa model PBL efektif dalam kemampuan berpikir kritis siswa. Rata-rata nilai pre-test pada kelas eksperimen 60, sedangkan kelas kontrol 62,5. Setelah diberikan perlakuan, nilai post-test kelas eksperimen menjadi 85,4, sementara kelas kontrol 74,2. Hasil uji-t sampel menunjukkan nilai signifikansi 0,001 (p < 0,05), terdapat perbedaan signifikan kedua kelompok. Nilai Uji n-gain mencapai 59,70% yang artiya model PBL pada berpikir kritis siswa cukup efektif dibandingkan model konvensional yang hanya 45,55% yang artinya kurang efektif untuk diterapkan. Model ini dapat menjadi alternatif pembelajaran inovatif yang interaktif dan berpusat pada siswa, sehingga direkomendasikan untuk diterapkan dalam pembelajaran matematika disekolah dasar.]]>
