This paper evaluates the effects of a remedial education programme implemented in Spain between 2005 and 2012 that offered after-school classes for underperforming students from poor socioeconomic backgrounds. We use two different estimation strategies, re-weighting estimators and propensity score matching, and address the existence of selection bias. We find that this programme had a substantial positive effect on children's academic achievement: the probability of falling behind the general progress of the group declined by between 3.5 and 6.4 percentage points and mean reading scores increased by between 8.5 and 17.4% of one standard deviation: We also find that a larger exposure to the programme improves students' scores: whereas students in schools that participated in the programme for at most two years do not experience any significant positive effect, those in schools that participated for at least three years did. The programme significantly reduced the probability of belonging to the bottom part of the distribution (by between 3.2 and 7.7 percentage points) and improved mean scores (by between 8 and 21.5% of one standard deviation). Finally, we find that the impact of the programme is much stronger for students in rural schools than for students in urban schools. (C) 2017 Elsevier Ltd. All rights reserved.