We use quantitative and qualitative methods to investigate the links between participation in adult learning and self-efficacy, particularly for the subgroup of adults who had low levels of achievement at school. We focus on self-efficacy because it translates into a range of wider benefits and because it may afford protection from depression and other forms of social exclusion. Quantitative analyses of data from the National Child Development Study (NCDS) provide evidence for an association between taking courses and transformations in self-efficacy for all cohort members, but the association is greatest and the evidence is strongest for our subgroup. A related fieldwork project involving in depth interviews with 15 women with poor school attainment sampled from the NCDS provides insights into some of the processes that underlie the associations found: (i) perceptions of achievement in adult education increase self-efficacy; (ii) adult education leads to more challenging occupations, which build self-efficacy; (iii) resistance to participation in adult education is reduced as self-efficacy increases; and (iv) learning on the job can build self-efficacy, and although participation in employer-provided training courses does not appear to play an important role, it reflects engagement in occupations where the value of learning is recognized. The interviews also illustrate how school impacts on self-efficacy and motivation to learn throughout the life course, and how important background and life circumstances can be in shaping the impacts of adult learning on self-efficacy.