This study identifies reasons for the low attendance of a peer-tutoring scheme for English language learners at a Colombian university. In what may be the first study of its kind, the article draws on concepts from realist evaluation to analyse the data from semi-structured interviews with six EFL teachers and two peer tutoring scheme staff. The findings suggest the importance of regular communication between tutees and their English teachers for the success of such schemes. The study also identified other factors that impact low attendance such as the value of English, student anxiety, motivation, and institutional constraints. These findings have implications not only for the implementation of English language peer-tutoring programmes in other EFL contexts, but also for EFL teaching more generally. To boost participation rates in such programmes, the study recommends compulsory participation for struggling learners, teacher training in motivational strategies, and activities aimed at increasing stakeholder involvement.