<![CDATA[Abstrak: Penelitian ini dilatarbelakangi dari masalah yang terjadi pada murid kelas II sekolah dasar pada pembelajaran matematika materi pengukuran berat dan waktu. Berdasarkan hasil observasi, sebagian besar murid masih mengalami kesulitan dalam memperkirakan hasil pengukuran, menjelaskan alasan dari jawaban yang diberikan, serta menarik kesimpulan dari kegiatan pengukuran yang dilakukan. Penelitian ini bertujuan untuk meningkatkan ketercapaian indikator kemampuan penalaran matematis murid kelas II sekolah dasar. Jenis penelitian yang digunakan adalah Penelitian Tindakan Kelas (PTK) dilaksanakan dalam dua siklus, dengan tahapan meliputi perencanaan, pelaksanaan, observasi dan refleksi. Subjek penelitian adalah 18 murid kelas II SDN Bareng 1. Teknik pengumpulan data menggunakan tes kemampuan penalaran matematis (4 butir soal uraian), observasi, dan dokumentasi. Analisis data dilakukan secara kualitatif dan kuantitatif dengan kriteria keberhasilan indikator ≥75%. Hasil penelitian menunjukkan bahwa model Discovery Learning berbantuan media Exploration Box dapat meningkatkan kemampuan penalaran matematis murid. Hal ini ditunjukkan dengan peningkatan rata-rata kemampuan penalaran matematis murid pada setiap siklus, yaitu dari pra siklus (60,5%), Siklus I (82,25%), hingga Siklus II (86,25%). Peningkatan juga terlihat pada keaktifan murid dari 45% (pra siklus) menjadi 78% (Siklus I) dan 88% (Siklus II). Meskipun terjadi penurunan pada indikator memperkirakan dugaan dari 79% pada Siklus I menjadi 76% pada Siklus II akibat keabstrakan materi durasi waktu, pencapaian tersebut tetap memenuhi kriteria keberhasilan. Berdasarkan hasil tersebut, dapat disimpulkan bahwa penerapan model Discovery Learning berbantuan media Exploration Box berkontribusi positif dalam meningkatkan kemampuan penalaran matematis serta keaktifan belajar murid kelas II sekolah dasar pada materi pengukuran berat dan waktu. Abstract: This study addresses issues encountered by second-grade elementary school students during mathematics lessons on weight and time measurement. Observations revealed that most students struggled to estimate measurement results, explain the reasoning behind their answers, and draw conclusions from measurement activities. The study aimed to enhance the achievement of indicators for mathematical reasoning abilities of second-grade elementary school students. A Classroom Action Research (CAR) design was employed, conducted over two cycles comprising planning, implementation, observation, and reflection stages. The research subjects were 18 second-grade elementary school students at SDN Bareng 1. Data collection techniques included tests (4 essay items based on reasoning indicators), observation, and documentation. Data analysis was conducted both qualitatively and quantitatively with a success criterion of ≥75%. The results indicate that the Discovery Learning model, supported by Exploration Box media, can improve students mathematical reasoning abilities. This is evidenced by the increase in the average mathematical reasoning ability of students across each cycle, from pre-cycle (60.5%), Cycle I (82.25%), to Cycle II (86.25%). Improvements were also observed in student active engagement, rising from 45% (pre-cycle) to 78% (Cycle I) and 88% (Cycle II). Although the indicator for estimating conjectures decreased from 79% in Cycle I to 76% in Cycle II due to the increased abstractness of time duration topics, it still met the success criteria. Based on these findings, it can be concluded that the implementation of the Discovery Learning model using Exploration Box media positively contributes to enhancing the mathematical reasoning abilities and learning engagement of second-grade elementary school students regarding weight and time measurement.]]>
