Background: Self-efficacy, or the beliefs learners hold about what they can do, develops largely from how learners perceive and interpret four main sources of information: mastery experiences, vicarious experiences, social persuasions and physiological and affective states. Although the relationship between these sources and self-efficacy is well-established, less is known about the factors that may influence how early adolescent learners perceive and interpret information from these sources. Aims: The purpose of this study was to investigate how the predisposition of perfectionism might predict how learners perceive efficacy-relevant information in the domain of math. Methods: Using a correlational design, this study considered whether perfectionism was associated with how middle school students (N = 1683) perceive information from the four hypothesized sources of self-efficacy. Participants completed a paper-based survey at two time points. Perfectionism was measured at Time 1. Self-efficacy and its sources were measured at Time 2. Structural equation modelling techniques were used to examine the relationship between factors. Results and Conclusions: Students who held themselves to high standards (i.e., greater self-oriented perfectionism) reported higher levels of mastery experiences, vicarious experiences, social messages and self-efficacy. Conversely, students who felt external pressure to be perfect (i.e., socially prescribed perfectionism) reported lower levels of mastery experiences, vicarious experiences and self-efficacy, as well as higher levels of negative physiological and affective states. The relationship between perfectionism and self-efficacy was partially mediated by students' perceptions of mastery. This study extends the current literature on the sources of math self-efficacy in early adolescence by showing how a predisposition like perfectionism is associated with how adolescent learners perceive and interpret efficacy-relevant information.