We meta-analyze enrollment, attendance and dropout effect estimates from forty two references of conditional cash transfer program evaluations in fifteen developing countries. Average effect sizes for all outcomes in primary and secondary schooling are statistically different from zero. Average effect sizes for secondary enrollment, attendance and dropout are larger than those for primary.  For all outcomes and schooling levels, there is considerable heterogeneity in effect sizes. Programs with more generous transfers have larger primary and secondary enrollment effects.  Programs that condition benefit receipt on achievement and pay transfers less frequently than monthly, exhibit larger enrollment and attendance effects. Effect sizes are no different in programs with random assignment.