Abstract Conditional cash transfer programmes have expanded in developing countries as a way to foster human capital accumulation. Despite evidence of these programmes' positive impact on school enrolment, little is known about their impact on school achievement. This study estimated the effect of Familias en Acción on school achievement. It found that the programme has a positive effect on school achievement for children aged seven to 12 living in rural areas. However, the study found a negative effect on the school achievement of adolescents, particularly those living in rural areas. Possible mechanisms of these effects are explored and discussed. Keywords: programme evaluationacademic achievementinternational educationconditional cash transfers Notes 1. The index, an indicator of economic well-being, is a function of a set of household demographic characteristics and variables related to the consumption of durable goods, human capital endowments, and current income. This index is divided into six strata, with SISBEN 1 corresponding to extremely poor or indigent, SISBEN 2 to poor, and SISBEN 3 to near poor. 2. This index, used in Colombia as a poverty indicator, comprises the following variables: schooling of household head, average schooling of individuals older than 12, school enrolment of children, main material of house walls, main material of house floor, mode of sewage disposal, access to water, cooking fuel, mode of garbage disposal, proportion of children aged under six, and number of individuals per room. 3. Durables include refrigerator, sewing machine, television, music equipment, fan, blender, kerosene lamp, and electric generator. 4. Results reported on Table 2 and throughout the paper are unweighted. The analyses were also done using sampling weights, and the results do not change. 5. Instrumental variables analyses with binary instrument and treatment variables can be thought of as a special case of a principal stratification analysis, as can be seen in Angrist, et al. (Citation1996). We cannot use instrumental variables here, however, both because the exclusion restriction might be violated and also because we do not have test scores on students not enrolled. 6. The TFB group has been exposed to the programme for a shorter time because it was introduced for them later than for the TIB group. Thus, whereas the TIB group had received an average of $1,009,255 in subsidies by the first follow-up, the TFB group had only received an average of $760,000. Likewise, the TFB group has been exposed to an average of six months less than the TIB group.