Most discussion of after-school programs in shanty towns has focused on estimating their average effects. The results of these programs are inconclusive and the explanation may be that the effects are heterogeneous. In this paper, we study the influence of how heterogeneity in the type of parents involved in the program affects the performance of their children at school. We measure performance at school according to academic achievement, behavior and grade retention. In line with previous literature, we employ the number of books at home as a proxy for parent type. By using random assignment to evaluate an after-school program in a developing-country shanty town, we find that it is effective in raising children’s school achievement for those with a committed parent type. Thus, this paper provides evidence that the knowledge of the distribution of effects is crucial to guiding public policy and it is not enough just to change the environment in which young people spend their after school hours, increasing time in safe, supervised settings, it is also necessary to take parenting type into account.