Influencing major education policies in the US such as school vouchers and charter schools, market theory assumes that organizational autonomy, parental choice, and competition between schools improve the quality of education. However, whether those policies can influence the instructional core of schools is not well understood. Comparing private and public schools offers an opportunity to examine whether market-oriented assumptions hold in practice. Relying on institutional theory, this study examines whether public and private schools differ in their instructional quality and whether such differences translate into achievement advantages in the US. Using Trends in International Mathematics and Science Study (TIMSS) surveys and achievement data, the study integrates structural equation modeling and propensity score matching to examine the latent construct of instructional quality and mitigate selection bias. Results indicate similar instructional quality in public and private schools explaining comparable student achievement by school type. Barriers to instructional change through market-oriented reforms are discussed.