We analyse the prevalence and effectiveness of out-of-school-time (OST) study programmes among secondary aged students, focusing on their potential for reducing socio-economic gaps in educational achievement. Compared to several extant studies, including the only prior study for Britain, whose findings could be affected by heterogeneous participation in the programmes, our results derive from a rich dataset with multiple controls for social background, personal motivation, and school characteristics. We find that programme participation in England is relatively low among students from families with long-term unemployed parents and those in routine occupations. Participation is also lower outside London, and especially outside large cities. Our results show that OST programmes, as long as they are teacher-led, are moderately effective in improving the academic performance at the end of lower secondary education as measured by the GCSE total score. Teacher-led OST programmes compensate for previous social disadvantage. The policy implications include a focus on expanding programme availability and on incentives for participation, and attention to the regional disparities.