This study examined whether and how attending university-based teacher education programmes may alter EFL teachers' self-efficacy. Comparisons were drawn across teachers with no academic credentials in L2 teacher education (uncertified teachers), teachers with Bachelor of Arts in L2 teacher education (BA teachers) and teachers with master of art in L2 teacher education (MA teachers). Quantitative data were collected from 150 Iranian EFL teachers using Teachers' Self-Efficacy Scale and supplemented by gaining insights from a smaller sample of teachers and teacher educators through focus group and individual interviews respectively. The results of one-way ANOVA revealed that, save for instructional strategies, B.A./M.A. teachers significantly scored better than their uncertified counterparts in the self-efficacy subscales as well as overall self-efficacy. No measurable discrepancy was however detected between B.A. and M.A. teachers' self-efficacy. Analysing the interview data, on the other hand, indicated that L2 teacher education programmes improved teachers' self-efficacy through presenting opportunities for knowledge base development, exposure to various teaching models and provision of professional advice. Conversely, M.A. programmes had no superiority over B.A. teacher education due to their theory-driven nature and inadequate infrastructure. The findings are discussed based on the range and frequency of self-efficacy sources incorporated in L2 teacher education programmes.