Process-oriented child monitoring (POM) deals with systematic monitoring of the observed learning needs of children in early childhood education by teachers. Between 2017 and 2021, a teacher professional development trajectory was implemented using POM in ethnically diverse preschools in Central Vietnam. These preschools typically consist of disadvantaged children at risk of barriers to classroom activity engagement. This study evaluates the effectiveness of POM using a pre- and posttest research design with a treatment and control group. Participants (N = 339) in the study were assigned to the treatment or control group using a clustered-randomized sampling approach. Whereas Kinh children rarely occur in the school population, the analysis focuses on ethnic minorities only in both treatment and control groups. Results indicate that POM is promising in increasing holistic child development. Five-year-old girls show most progression in cognitive functioning and socio-emotional development, while boys at this age indicate advances in socio-emotional development and health behaviors. Further evidence indicates that changes in teaching children from poor households play out much faster for child development, as opposed to what is observed among wealthier households.