Randomization at the school level
Of the eight invited schools, we randomly chose four to participate in the program by simple random sampling without replacement. We collected baseline information from both the treatment and control schools in February 2015. All 12th grade high school students took part in the intervention in the treatment schools. We also considered 11th grade students attending both treatment and control schools as an additional comparison group. In the presence of positive spillover effects from the treated, considering this additional comparison group would only make our results just more conservative. All students attending 12th grade in the treated schools had to participate in the program as part of regular school obligations. This limits the concerns about selection bias due to non-random attrition. The mandatory feature also allows us to estimate average treatment effects, instead of intent to treat estimates.