<![CDATA[ABSTRACT: This study was motivated by preliminary observations at UPTD SMP Negeri 1 Gunungsitoli Alo’oa, which indicated that students’ mathematical reasoning skills were still low, while the mathematics instructional materials used were relatively limited. Based on this situation, the study aimed to: (1) analyze the validity of project-based Student Worksheets (LKS), (2) assess their practicality, and (3) evaluate their effectiveness in learning. The research employed a development approach using the ADDIE model (Analysis, Design, Development, Implementation, Evaluation), utilizing test instruments, validation questionnaires, and response surveys, with both qualitative and quantitative data analyses. The results demonstrated that the project-based LKS were valid, practical, and effective. Validity scores were 84.72% from the first content expert (valid), 87.50% from the second content expert (very valid), 91.67% from the language expert (very valid), and 88.54% from the media expert (very valid). Practicality scores were 72.22% in individual trials (practical), 84.83% in small group trials (very practical), and 88.11% in field trials (very practical). The effectiveness of the LKS was reflected in the students’ average mathematical reasoning score of 87.88 (very good) and a classical completeness of 86.36% (very effective). Therefore, the project-based LKS are deemed suitable for enhancing the mathematical reasoning skills of junior high school students. ABSTRAK: Penelitian ini dilatarbelakangi hasil observasi awal di UPTD SMP Negeri 1 Gunungsitoli Alo’oa yang menunjukkan bahwa kemampuan penalaran matematis siswa masih rendah, sementara bahan ajar matematika yang digunakan tergolong terbatas. Berdasarkan kondisi ini, penelitian bertujuan: (1) menganalisis validitas Lembar Kerja Siswa (LKS) berbasis proyek, (2) menilai kepraktisan LKS, dan (3) mengevaluasi efektivitasnya dalam pembelajaran. Metode yang digunakan adalah penelitian pengembangan dengan model ADDIE (Analysis, Design, Development, Implementation, Evaluation), menggunakan instrumen tes, angket validasi, dan angket respon, dengan analisis data kualitatif dan kuantitatif. Hasil penelitian menunjukkan bahwa LKS berbasis proyek terbukti valid, praktis, dan efektif. Validitas LKS memperoleh skor 84,72% dari ahli materi pertama (valid), 87,50% dari ahli materi kedua (sangat valid), 91,67% dari ahli bahasa (sangat valid), dan 88,54% dari ahli media (sangat valid). Kepraktisan LKS ditunjukkan dengan skor 72,22% pada uji perseorangan (praktis), 84,83% pada uji kelompok kecil (sangat praktis), dan 88,11% pada uji lapangan (sangat praktis). Efektivitas LKS terlihat dari rata-rata kemampuan penalaran matematis siswa sebesar 87,88 (sangat baik) dan ketuntasan klasikal 86,36% (sangat efektif). Dengan demikian, LKS berbasis proyek layak digunakan untuk meningkatkan penalaran matematis siswa SMP.]]>
