Purpose: The purpose of this study is to evaluate the application of quality management systems (QMS) based on international standards of quality in education (ISO 9001:2008) and ascertain the influence of this quality model on primary and secondary schools in Spain. Design/methodology/approach: The study was conducted in 26 publicly funded, private schools in Spain. The research design was a three-phase, mixed-methods evaluation. In all, 809 teachers answered the main survey questionnaire in Phase 3, which was validated through expert reviews and exploratory factor analysis against two theoretically derived dimensions of quality. The total scores of the two dimensions demonstrated Cronbach's alpha reliability estimate > 0.95. A discriminant function analysis was applied next to compare three groups of schools based on teachers' QMS ratings, using students' achievement and other school quality indicators as predictors. Findings: The QMS model was perceived to have contributed to improvements in documentation and management through evaluation, continuous improvement processes, the schools' external image, management of resources and user satisfaction levels. Some of the improvements lasted over time. The schools rated as "high" by teachers on QMS implementation levels had better educational outcomes, as well as user perception and satisfaction levels, as compared to schools rated as "low". Drawbacks of the QMS model were perceived as high bureaucratic workloads and a top-down management culture. Practical implications: The findings suggest that ISO standards of QMS can be adopted in primary and secondary education institutions successfully, and that they are suitable for improving schools and educational systems overall. Originality/value: The study's originality lies in the demonstrated outcomes of the QMS approach, originally created for industrial environments, in a large Spanish primary and secondary education institution using a three-phase, mixed-methods design.