<![CDATA[Natural and Social Sciences (IPAS) instruction in primary schools is frequently dominated by teacher-centered lecturing that primarily emphasizes theoretical rote memorization. Conventional classroom assessment also tends to prioritize lower-order cognitive mastery, leaving students' science process skills underdeveloped. Empirical research examining the integration of problem-based approaches to explore the properties of matter in elementary classrooms remains essential to demonstrate its effectiveness in fostering scientific inquiry. Addressing this pedagogical gap, this study aims to investigate the effect of the Problem Based Learning model on the science process skills of fourth-grade students in IPAS instruction at SD Swasta Katolik Diski during the 2025/2026 academic year. This quantitative study utilized a pre-experimental one-group pretest-posttest design involving all 34 fourth-grade students selected through a total sampling technique. The research instruments comprised an essay test measuring science process skills, validated theoretically and empirically, alongside systematic observation sheets to record procedural inquiry behaviors. The empirical findings demonstrated that the students' mean score increased significantly from the poor category at the baseline assessment to the very good category at the post-test evaluation. Inferential statistical testing utilizing the paired sample t-test revealed that the calculated t-value surpassed the critical t-table value at the 0.05 significance level, leading to the rejection of the null hypothesis. Consequently, implementing the Problem Based Learning model exerts a positive and significant effect on enhancing elementary school students' science process skills. ABSTRAK Pembelajaran Ilmu Pengetahuan Alam dan Sosial (IPAS) di sekolah dasar kerap didominasi oleh metode ceramah satu arah yang berfokus pada hafalan teori semata. Praktik evaluasi pembelajaran juga masih condong menilai aspek kognitif tingkat rendah, sehingga keterampilan proses sains peserta didik belum terlatih secara optimal. Penelitian mengenai model pembelajaran berbasis masalah pada materi sifat benda di tingkat sekolah dasar masih perlu diperluas guna membuktikan efektivitasnya dalam memicu keterampilan penyelidikan ilmiah. Berangkat dari kesenjangan tersebut, penelitian ini bertujuan untuk mengetahui pengaruh penerapan model Problem Based Learning terhadap keterampilan proses sains peserta didik pada mata pelajaran IPAS kelas IV SD Swasta Katolik Diski Tahun Ajaran 2025/2026. Penelitian kuantitatif ini menerapkan rancangan pre-experimental design dengan bentuk one-group pretest-posttest design yang melibatkan seluruh peserta didik kelas IV sebanyak 34 orang yang dipilih melalui teknik total sampling. Instrumen penelitian terdiri atas tes esai keterampilan proses sains yang telah tervalidasi secara teoretis maupun empiris, serta lembar observasi aktivitas penyelidikan ilmiah. Hasil pengujian membuktikan bahwa perolehan nilai rata-rata peserta didik meningkat secara signifikan dari kategori kurang pada pengukuran awal menjadi kategori sangat baik pada pengukuran akhir. Analisis inferensial menggunakan uji paired sample t-test membuktikan bahwa nilai melampaui nilai pada taraf signifikansi 0,05, yang menegaskan penolakan hipotesis nol. Dengan demikian, penerapan model Problem Based Learning terbukti memberikan pengaruh yang positif dan signifikan terhadap penguatan keterampilan proses sains peserta didik sekolah dasar. ]]>
