There have been increasing calls for career development interventions that take the local context into account while providing a firm theoretical basis to engage with the career processes and attributes of individuals coming from diverse backgrounds. The goal of this study was to determine the effect of a career intervention programme derived from Social Cognitive Career Theory on the career decision-making self-efficacy of Grade 11 learners at three schools with diverse socio-economic backgrounds in the Eastern Cape. Using a quasi-experimental design, measurements were taken at a pretest, post-test and a follow-up occasion 8 weeks after the completion of the programme in a sample of 222 learners using the Career Decision-Making Self-Efficacy Scale. The study demonstrated that the career decision-making self-efficacy of the intervention group improved significantly subsequent to the career intervention programme underscoring the value of the career intervention programme. Although the current study demonstrated a medium effect on the intervention group by the end of the intervention, the time period of the programme may not have been long enough to sustain the impact 8 weeks after the completion of the programme. This may suggest that a longer intervention period or intermittent reinforcement such as booster sessions may be needed to sustain the effect. The study confirms that a group-based career development programme, designed specifically for the South African context, can serve as an essential tool to help high school learners from different socio-economic backgrounds enhance their career maturity expressed in terms of their career decision-making self-efficacy.