Monitoring data are generally collected as a by-product of the process of monitoring program implementation. Yet this rich source of data have not been exploited to assess the effectiveness of the program. In this paper the authors use detailed administered data from a large-scale, community-based nutrition program in Madagascar to argue that this data can be used to estimate the differential effect of increased exposure to the program and study how these returns to exposure evolve over time. They find that the returns to exposure are positive: communities exposed for an additional one or two years display on average lower malnutrition rates of around 7-9 percentage points. And they find that the returns decrease as time and duration increase, although they do not dissipate to zero. These results are consistent with the hypothesis that the returns to the program reflect learning effects from the intervention. Finally, the results show higher differential returns to the program in poorer areas and areas more vulnerable to diseases. These findings have important implications for how such programs should be scaled-up within a country.