Direct subsidy scheme (DSS) schools are a product of Hong Kong's market-oriented educational reform, mirroring global reform that champions parental choice and school marketization. Such schools have greater autonomy in matters of curricula, staffing, and student admission. Although advocates of the DSS credit it with increasing educational diversity and competition, little empirical is available to back up such claim. In this study, we use data from the Program for International Student Assessment to compare student achievements in DSS schools with those in traditional public schools. We find that while DSS students' test scores in math, reading, and science have improved significantly over time, though the variation is much greater. Changes in mean performance have been anchored by a substantial change in student composition. DSS schools have a higher proportion of students with high socioeconomic status than with medium and low socioeconomic status. DSS schools also amplify the effects that family background have on student achievement. These findings raise concerns that the DSS approach favors a small minority of students.