This study examines the roles played by student characteristics, school resources and practices, peer effects, and province fixed effects in accounting for differences in the academic outcomes of private and public high school students. Private high school students score significantly higher than public high school students on reading, mathematics, and science assessments at age 15, and have higher levels of educational attainment by age 23. Two factors consistently account for these differences. Students who attended private high schools were more likely to have socio-economic characteristics positively associated with academic success and to have school peers with university-educated parents. Province of school attendance accounted for a substantial portion of the differences in academic outcomes measured in high school (i.e., test scores and high school graduation rates), but generally not at the postsecondary level. School resources and practices accounted for little of the differences in academic outcomes.