they had an opportunity to enroll in playgroups at the appropriate age, starting at age 3 and continuing through age 4. Thus, the two cohorts differed in their likelihood of being exposed to playgroups at the appropriate age.

Our data allow us to track the development outcomes for both cohorts at ages 5 and 8. To control for children’s baseline development, we use measures of child development before exposure to playgroups. For the younger cohort, we have data on child development measures from when they were 1 and 2 years old. For the older cohort, we have data on child development measures from when they were 4 years old. We use a comprehensive set of child development outcomes that measure both cognitive and socio-emotional development. In addition, we capture children’s performance on a test of language, mathematics and abstract reasoning in primary school. Together, these measures allow us to trace out early development on a variety of dimensions.

We build upon previous work by Brinkman et al. (2017b), which analyzed the impact of the project on the older cohort. In this paper, we conduct three new analyses. First, we present child development outcomes for the younger cohort at ages 5 and 8. Second, we present new results for the older cohort using primary school test scores. Third, we contrast the developmental trajectories between the two cohorts. We explore how features of project implementation as well as different rates of exposure to playgroups at the appropriate age may have contributed to the contrasting results between the two cohorts.

This paper also contributes to research on the generalizability of impact evaluations in early childhood education. Preschool interventions in developing countries have produced a wide range of effect sizes, prompting both researchers and policy makers to question the generalizability of these findings (Tanner et al., 2015). In particular, it is difficult to understand what causes these variations since each preschool program is different in terms of what the program provides, how the program is implemented and where the program is carried out. In this paper, we are able to hold constant the program content (what) and the study context (where) but vary the implementation (how) experienced by two cohorts of children. In doing so, we document the extent to which program impacts may vary as a result of differences in project implementation.

This paper proceeds as follows: The second section describes the Indonesia Early Childhood Education and Development (ECED) Project. The third section explains the data we use in our analysis. The empirical strategy is described in the fourth section. The fifth section provides the empirical results and the sixth section compares the impacts on the younger cohort and older cohorts. The seventh section presents a cost-benefit analysis based on our intent-to-treat estimates of additional years of schooling completed by those living in project villages. The final section concludes with a discussion of the findings and their implications for future work.

# **2. Indonesia Early Childhood Education and Development (ECED) Project**

The goals of the Indonesia ECED Project were to increase access to early childhood services and to increase children’s school readiness in rural villages. The project consisted of three components. First, a community facilitator raised awareness about the importance of early childhood services and shared information about how to prepare a proposal for the block grants available through the project.

Second, block grants were provided to each village, in the amount of USD 18,000 per village over three years. Villages could use the grant to establish or support up to two early childhood education centers. No more than 20 percent of the grant could be spent on new infrastructure. The most common form of services established were playgroups, which are early childhood education services catered to children ages 3 and 4 before they enroll in 2