Academic data management in secondary schools frequently encounters operational challenges such as processing delays and high risks of human error due to manual grade calculation. This study aims to design and implement a web-based academic information system capable of predicting cumulative final grades and automating student ranking determinations at SMA PGRI Larantuka utilizing the Regression Decision Tree algorithm. The system development methodology adopted the sequential Waterfall model, comprising requirement analysis, system architecture design, code implementation, verification testing, and operational maintenance. Empirical evaluation of the regression model using 36 historical student records (29 training sets and 7 test sets) indicated exceptional predictive precision, yielding a Mean Squared Error (MSE) of 3.15 and a coefficient of determination () of 0.88 (88%). Functional validation via Blackbox Testing achieved a 100% valid status across all test suites, while the User Acceptance Test (UAT) conducted with 28 educators and academic staff generated an approval rating of 93.14% (Very Good category). The empirical results substantiate that embedding the Regression Decision Tree algorithm within a web-based educational management system significantly improves computational efficiency, predictive accuracy, and procedural objectivity in secondary school academic assessments. ABSTRAK Pengelolaan data akademik di sekolah menengah sering kali masih menghadapi kendala keterlambatan dan potensi kesalahan manusia (human error) akibat rekapitulasi nilai yang dilakukan secara manual. Penelitian ini bertujuan untuk merancang dan membangun sistem informasi berbasis web yang mampu memprediksi nilai akhir serta menentukan peringkat siswa secara otomatis di SMA PGRI Larantuka menggunakan algoritma Pohon Keputusan Regresi (Regression Decision Tree). Metode pengembangan sistem mengadopsi model Waterfall, yang mencakup tahap analisis kebutuhan, perancangan, implementasi, pengujian, dan pemeliharaan. Evaluasi model regresi berbasis 36 data akademik historis (29 data latih dan 7 data uji) menunjukkan performa yang sangat presisi dengan nilai Mean Squared Error (MSE) sebesar 3,15 dan koefisien determinasi () sebesar 0,88 (88%). Pengujian fungsionalitas menggunakan Blackbox Testing menghasilkan 100% status valid, sedangkan pengujian penerimaan pengguna (User Acceptance Test / UAT) terhadap 28 guru dan tenaga pendidik memperoleh persentase kelayakan sebesar 93,14% (kategori Sangat Baik). Hasil penelitian membuktikan bahwa penerapan algoritma Pohon Keputusan Regresi pada sistem E-Penilaian berbasis web mampu meningkatkan efisiensi, akurasi, dan objektivitas evaluasi akademik siswa secara terstruktur.
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