Choice of Ontario high schools and student sorting by ability

To what extent can offering more choice in schooling lead to ‘cream skimming,’ or the sorting of students by ability? I study whether increased choice leads to student sorting by ability into high schools in the Greater Toronto Area. On average, 41% of students ‘opt out’ of the high school to which they would normally be assigned based on their residence. Students are more likely to opt out in areas where accessibility to other schools is greatest due to population density and explicit ‘open enrolment’ policies. While students of higher ability are generally more likely to opt out, an interaction term between school choice and ability is insignificant, suggesting that increased choice does not have differential impacts by student ability. Findings are robust to changes in assumptions about instrument exogeneity.