Purpose: Desertion rates in Colombian universities remain unacceptably high. In the field of foreign languages, academic failure is particularly concerning since English language instruction is compulsory in most universities. To address the issue of poor student performance and high dropout rates, the University of Colombia has set up a peer tutoring scheme (PTS) for English as a foreign language (EFL) students in order to inform programme development. The paper aims to discuss this issue. Design/methodology/approach: The study was informed by realist evaluation principles. Qualitative in-depth interviews were conducted with eight PTS stakeholders supplemented by documentary analysis of the programme's publicity material on the PTS website. The data were analysed using thematic analysis. Findings: Findings reveal discrepancies between the "espoused theory" about how the programme operates and the "theory-in-use". In particular, according to stakeholders, the programme does not appear to be used by many of those EFL students who would benefit from it, which suggests that the programme is not as effective as it could be. Student and teacher contextual factors and mechanisms may explain the reasons for issues with programme effectiveness. Research limitations/implications: Formative evaluations such as the current study can provide rich contextual information, but cannot be generalised to other settings. Also, this study does not explore the perspective of peer tutors and tutees, which means key variables may have been overlooked. Further research into the perspectives of tutors and tutees would therefore be needed to firm up these conclusions. Practical implications: Due to the scarcity of literature into EFL peer tutoring interventions in higher education (HE), it is hoped that these findings will have relevance for similar contexts. The current evaluation highlights the influence of contextual factors such as willingness to ask for help, student motivation, student priorities, tutor credibility, teacher workload, timetabling and scheduling issues and involvement from teachers on the success of open-access peer tutoring programmes for EFL students in higher educational settings. Originality/value: As far the researcher is aware, this is the first evaluation of an EFL peer tutoring programme in a private HE context in Colombia, and one of only a handful of studies into EFL peer tutoring programmes. The findings therefore have implications for those working in similar contexts.