This dissertation examines the role early childhood education (ECE) plays in shaping children’s educational trajectories by focusing on one country that is experiencing the most rapid and massive expansion of preschool access in sub-Saharan Africa: Ethiopia. This thesis consists of three distinctive but interconnected papers. The first paper assesses changes in the relationship between preschool attendance and students’ early grade reading achievement during the large-scale expansion of public preschool (O-Class) in Ethiopia. It leverages two Early Grade Reading Assessment (EGRA) datasets that straddle the reform period from 2010 to 2016, during which pre-primary enrolment rates soared by nearly ten times. The results suggest that the large-scale preschool expansion strengthened the role of preschool attendance in predicting second- and third-grade students’ reading performance. The second paper further examines the differential influence of preschool by various child, family, and school characteristics. Despite the benefit of increased access to preschool on average, the results show that the preschool benefits were greater for affluent children, which suggest that the largescale expansion of preschool may come at the expense of equitable gains between advantaged and disadvantaged children. The third paper investigates how the relation between preschool attendance and student outcomes evolves from early childhood to adolescence. The results indicate that preschool attendance led to significant improvement in academic achievement in receptive vocabulary and language and increased educational attainment by age 15, the age at which most students are transitioning to secondary school. Moreover, the results highlight the importance of quality of preschool, as well as subsequent school experiences. These quality dimensions have the potential not only to determine the preservation of preschool benefits but to facilitate students’ positive academic trajectories from early childhood through adolescence. Directions for future research and policy implications related to ECE in Ethiopia are discussed.