The need to improve student success in community colleges has resulted in a growing interest in developmental mathematics. Yet there remains a need to understand the motivations and beliefs of developmental mathematics students in order to cultivate their success. Self-efficacy has been identified to be a predictor of student success. Little is known about the antecedents or sources of self-efficacy of students enrolled in remedial courses at community colleges and how their self-efficacy can be bolstered through such courses. An instrument was developed to measure sources of mathematics self-efficacy and was originally tested with middle school students. Using a sample of 439 students, it was found that a scale which measures sources of self-efficacy is psychometrically acceptable for adults completing mathematics remediation. Our results indicated that the four theorised sources of self-efficacy explained a large percentage of the variance in mathematics skill self-efficacy for our sample. As hypothesised by others, mastery experiences was the best predictor of self-efficacy but all sources influenced mathematics skills self-efficacy.