Engaging culturally diverse learners (CDLs) in mathematics remains a crucial challenge in U.S. secondary education. This qualitative case study examined the impact of Culturally Responsive Mathematics Teaching (CRMT) on student engagement in a high school geometry class. Grounded in culturally responsive teaching (Gay, 2002; Ladson-Billings, 1995) and informed by the Standards for Mathematical Practice, the study explored behavioral, emotional, and cognitive engagement (Fredricks et al., 2004) as students participated in CRMT-aligned lessons. Data were collected from eight student participants through semi-structured interviews, lesson reflections, classroom observations, and supporting artifacts. Analysis employed descriptive, emotional, versus, and process coding, refined through constant comparison and crystallization. Findings revealed that CRMT strategies fostered engagement through four interrelated themes: (a) hands-on activities and group work that sustained participation, (b) opportunities for choice and collaboration that enhanced agency, (c) culturally relevant contexts that promoted confidence and meaningful connections, and (d) supportive relationships and classroom climate that encouraged persistence. Students reported increased confidence, collaboration, and risk-taking when instruction was culturally affirming and connected to real-world applications. This study contributes to scholarship on culturally responsive pedagogy by illustrating how CRMT can elevate engagement in secondary mathematics while highlighting implications for equity in STEM pathways.