As competition in the secondary education market grows, increasing service quality to ensure parents' satisfaction and loyalty is crucial to the future success of secondary schools. As parents of secondary school students (PASESS) are not the direct recipients of educational service, the main goal of this research was to investigate the mediating role of transformative quality between assessment of core educational quality and parents' satisfaction and loyalty. Structural equation modeling was used to analyze the data collected from 209 PASESS in Vietnam. The results showed that, similar to previous research, satisfaction is the strongest determinant of loyalty. Attitude and behavior were the only components of core educational quality that had a direct impact on loyalty. The findings also revealed that the relationship between competence and curriculum and core educational quality and loyalty is mediated by transformative quality and satisfaction. The practical implications and theoretical contributions of the research findings are also discussed.