<![CDATA[ABSTRACT Mathematics learning on the topic of Straight-Line Equations continues to present challenges when students are not provided with sufficient opportunities to construct and explore concepts independently. This condition motivated the development of an inquiry-based mathematics learning module for eighth-grade students at SMP Negeri 5 Semarang. The product was developed through a Research and Development approach using the ADDIE framework, which consists of the Analysis, Design, Development, Implementation, and Evaluation stages. The development process involved expert validators, a mathematics teacher, and eighth-grade students, while the research data were collected through observation, interviews, documentation, questionnaires, and tests of mathematical conceptual understanding. The product evaluation yielded a validity score of 93%. Its implementation also received very positive responses from the teacher at 96.6% and from students at 85.7%, indicating that the module was practical for classroom use. During the implementation stage, the experimental class achieved 80% classical learning mastery, compared with 65% in the class receiving conventional instruction, accompanied by a significant difference in students’ mathematical conceptual understanding. Taken together, these findings position the inquiry-based module as a valid, practical, and effective learning resource for encouraging students to actively construct mathematical concepts in the topic of Straight-Line Equations. ABSTRAK Pembelajaran matematika pada materi Persamaan Garis Lurus masih menghadapi persoalan ketika siswa belum memperoleh ruang yang cukup untuk membangun dan menelusuri konsep secara mandiri. Kondisi tersebut melatarbelakangi pengembangan modul pembelajaran matematika berbasis metode inkuiri bagi siswa kelas VIII SMP Negeri 5 Semarang. Produk dikembangkan melalui pendekatan Research and Development dengan kerangka ADDIE yang mencakup tahap Analysis, Design, Development, Implementation, dan Evaluation. Proses pengembangan melibatkan validator ahli, guru matematika, dan siswa kelas VIII, sementara informasi penelitian dihimpun melalui observasi, wawancara, dokumentasi, angket, serta tes pemahaman konsep matematis. Penilaian terhadap produk memperlihatkan tingkat validitas sebesar 93%. Penggunaannya juga memperoleh respons sangat baik dari guru sebesar 96,6% dan dari siswa sebesar 85,7%, yang mengindikasikan bahwa modul dapat diterapkan secara praktis dalam pembelajaran. Pada tahap implementasi, ketuntasan klasikal kelas yang menggunakan modul mencapai 80%, sedangkan kelas dengan pembelajaran konvensional mencapai 65%, disertai perbedaan kemampuan pemahaman konsep matematis yang signifikan. Rangkaian temuan tersebut menempatkan modul berbasis metode inkuiri sebagai bahan ajar yang valid, praktis, dan efektif untuk mendorong keterlibatan siswa dalam membangun pemahaman konsep matematis pada materi Persamaan Garis Lurus.]]>
