will refer to them as the **original households** , since their sampling took place back in 1997. Panel B in Table 1, shows the attrition resulting from the inability to locate some of the original households in the 334 selected localities. Larger households with more assets are more likely to be surveyed in 2017. Importantly, and central for the internal validity of the estimated effects, we show that the overall attrition described appears orthogonal to treatment (see _Table 2_ ). This latter result is reassuring in terms of causal identification of the treatments effects, however we should mention that those effects might not be applicable to the entire population of interest. Despite that concern we conjecture that the sampling framework adopted is likely to produce underestimates or conservative estimates of the effects as the sample, includes better off households to start with, and it is plausible that the program effects would be smaller for those households.

Next, using a list of all the individuals in the 1997 original households, surveyors asked for socio-demographic information about each of them, as well as for the new members living in the household (these would be offspring or other individuals entering the household after the 1997 survey round). Among the original set of individuals, a separate survey was designed for members that were in critical age groups at the time in which the program started. Three age groups of interest were then defined: (i) newborns in 1997-2000, since they were in a critical stage of development when the RCT took place; (ii) children 6 to 8 years old in 1997-2000, since they were about to enroll in school grades where the program’s conditionalities are most relevant; and (iii) children in sixth grade in 1997-2000, since the program’s positive effects in terms of later school enrollment appear to be concentrated in this critical grade.

Importantly, these individuals could be still living in the _original households_ , but they could have also moved out to form a new household (or joined an existing one). Contact information was recorded to track these individuals. This search process had a geographic limitation: interviews with individuals that moved out of the original household were only attempted if they settled in the same locality as the original household, within a short range of the original household’s locality<sup>9</sup> or in the three main metropolitan areas in Mexico (Mexico City, Monterrey and Guadalajara). As mentioned above, the households where these individuals were located could be either newly formed households (e.g. the individuals married or just decided to move out by themselves) or could be households that already existed and the individual decided to move in (e.g. moving with relatives). For the purpose of our analysis we define all these households as **new households** in the sense that they did not exist in the 1997 sample.

Surveyors were able to locate and interview 4,987 individuals in the relevant group ages: 2,105 of them were still in their original households and the remaining 2,882 were in new households. Of the individuals living in a new household, 4,207 interviews were not successfully completed, either because they moved to a household not accessible given the survey 9Given budgetary restrictions, households were searched in localities located within a 30 minute driving distance at most.

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