Penelitian ini dilatarbelakangi oleh kesulitan belajar Matematika (KBM) yang dialami siswa. Wawasan mengenai faktor-faktor yang menyebabkan KBM sangat penting sebagai dasar dalam merancang strategi peningkatan pembelajaran. Namun, penelitian yang secara khusus menggali penyebab KBM di jenjang Sekolah Menengah Atas (SMA) masih langka. Tujuan penelitian ini untuk mengeksplorasi faktor-faktor yang menyebabkan siswa mengalami KBM di SMA Nahdlatul Ulama 1 Tarakan. Penelitian kualitatif ini menggunakan pendekatan studi kasus dengan melibatkan enam partisipan yang dipilih berdasarkan hasil angket yang disebarkan kepada seluruh siswa. Data diperoleh melalui angket, dan wawancara yang dianalisis secara tematik. Temuan penelitian mengungkapkan 8 tema penyebab mengapa siswa mengalami KBM, yaitu: (1) anggapan bahwa belajar Matematika itu sulit, (2) suasana pembelajaran yang kurang kondusif, (3) kebiasaan belajar Matematika yang kurang, (4) kompetensi pedagogik guru yang kurang, (5) dukungan orang tua yang kurang, (6) kesulitan dalam menerapkan Matematika pada kehidupan sehari-hari, (7) sarana dan prasarana sekolah yang kurang memadai, dan (8) malu bertanya meskipun belum memahami materi. Hasil penelitian ini mengungkapkan urgensi terkait kompetensi guru. Guru diharapkan terus mengembangkan kompetensinya melalui penerapan metode pembelajaran yang inovatif dan sesuai dengan kebutuhan siswa, melakukan tes diagnostik untuk mengidentifikasi kemampuan awal dan kesulitan belajar siswa, serta membangun persepsi positif terhadap Matematika agar proses belajar berlangsung lebih efektif, menyenangkan, dan berkelanjutan.

This research is motivated by the difficulties in learning Mathematics (KBM) experienced by students. Understanding the factors that cause KBM is very essential as a basis for designing strategies to improve learning. However, research specifically exploring the causes of KBM at Senior High School (SMA) level is still scarce. The aim of this research was to explore the factors that cause students to experience KBM at Nahdlatul Ulama High School 1 Tarakan. This qualitative research used a case study approach involving six participants selected based on the results of a questionnaire distributed to all students. The data were obtained through questionnaires and interviews that were analyzed thematically. The research findings revealed 8 themes of factors why students experienced KBM, namely: (1) the assumption that learning Mathematics is difficult, (2) an unfavorable learning environment, (3) inadequate Mathematics learning habits, (4) insufficient pedagogical competencies of teachers, (5) lack of parental support, (6) difficulties in applying Mathematics to everyday life, (7) inadequate school facilities and infrastructure, and (8) reluctance to ask questions even when the material is not understood. The results of this study reveal the urgency related to teacher competencies. Teachers are expected to continuously develop their competencies through the implementation of innovative teaching methods that meet students' needs, conducting diagnostic tests to identify student initial abilities and learning difficulties, and fostering a positive perception of Mathematics so that the learning process can be more effective, enjoyable, and sustainable.