Ireland is experiencing a severe shortage of qualified teachers willing to deliver formal Computer Science (CS) curricula at second-level. This study compares the programming self-efficacy of non-formal and formal curricular teachers. Non-formal teachers deliver introductory computer science to upper second-level students, however, this is not part of state-sanctioned national curricula, thus varying in content and duration. Formal curricula teachers are those delivering the state-sanctioned national upper second-level computer science curriculum. In particular, their programming self-efficacy is measured at the point where the non-formal teachers had completed a year delivering informal content using an online training platform called CSLINC and the formal curricular teachers were about to embark on the delivery of formal curricula. The goal is investigating if CSLINC provides enough support so that informal teachers’ self-efficacy is comparable, at this point in time, to that of formal teachers. The hypothesis is that if they are comparable, CSLINC has contributed to developing their beliefs about teaching and instructional practices to support them to make the leap to formal curricula. We found a statistically significant difference between the non-formal curricular teachers and the formal curricular teachers (with a significant effect size). The self-efficacy of the non-formal curricular teachers was significantly lower than that of the formal curricular teachers, suggesting that one year of CSLINC alone might not sufficiently support teachers to undertake formal curricular delivery. Additional tailored Continuous Professional Development (CPD), formal or informal, may be necessary to improve teacher self-efficacy further.