The purpose of this study was to explore how mathematics teachers in urban schools serving disadvantaged communities develop their teaching self-efficacy and how teachers’ attribution beliefs were related to their interpretations of efficacy sources. Data from the semi-structured interviews indicated that mastery experiences and social persuasions paired with internal and controllable attributions were the most salient sources that positively influenced teachers’ teaching self-efficacy. Failures undermined teachers’ teaching self-efficacy only when they were attributed to internal and uncontrollable factors. When failures were attributed to internal and controllable factors, they did not undermine teaching self-efficacy. Considering social persuasions, when evaluative feedback was communicated in a hostile way and made teachers perceive uncontrollable attributions, it decreased mathematics teachers’ teaching self-efficacy. Vicarious experiences emerged as the third most influential source of teaching self-efficacy as vicarious experiences enabled struggling teachers to believe they could accomplish similar tasks. However, negative models lowered teachers’ self-efficacy when teachers perceived little control over the situation. The findings of the research revealed the processes and sources of teaching self-efficacy development as well as the intricate relationship between teaching self-efficacy and teachers’ attribution beliefs. The results not only advanced our understanding of teaching self-efficacy but also provided meaningful insights and practical implications for preparing and supporting teachers in schools serving disadvantaged urban communities. It also has important implications for policymaking regarding teacher retention and educational equity.