Mathematics teachers' preteaching experiences as mathematics learners can affect their identity and practice in supporting their own students' learning and motivation in mathematics. However, little empirical data exist on teachers' formative experiences to guide these assumptions, particularly how teachers draw on these experiences when teaching, motivating, and caring for underserved students of color. This exploratory sequential mixed-methods study examines the formative mathematical experiences of 12 teachers currently serving Black and Latinx adolescents in an urban school district with concentrated poverty. Semi-structured interviews allowed teachers to reflect on their formative experiences as mathematics students, structured classroom observations assessed their current classroom care practices as teachers, and finally, questionnaires and a standardized mathematics assessment were used to examine their students' (n = 329) mathematical outcomes. This integration of methods provided three levels of inquiry for triangulation and interpretation. Results showed that teachers developed an ethic of perseverance through their formative experiences, which closely tied to their mathematics identity. However, teachers' perceptions on what enabled them to persevere through challenges as students (i.e., people-support vs. personal-initiative) revealed clear differences in the emotional and instructional support techniques they provided in their classrooms and subsequently their students' sense of belonging in mathematics. Teachers who discussed the role of people-support in their formative reflections were more likely to possess a critical consciousness on the interpersonal and systemic forces that work against Black and Latinx adolescents and thus enact empathetic care patterns. Furthermore, their observed classroom care patterns mediated the relation between their formative experiences and their students' sense of belonging in mathematics.