Taking advantage of newly available data on a standardized national examination for secondary school students in Thailand, this study attempts to explain the variation in the average performance of students using school and local characteristics. Special emphasis is placed on trying to understand the asymmetric success factors of public and private secondary schools, and the possible effects of their coexistence. Results from a propensity score matching model suggest that private schools may create positive spillovers on the academic performance of students attending public schools located in the same district. The main implication from the research is that a more careful discussion about the impact of the ongoing education reforms on private schools is needed.