A new paper by David Card, Martin Dooley, and Abigail Payne looks at Ontario’s unique public school system, which includes secular public schools and Catholic public schools open only to Catholics, to estimate the impacts of school choice and school competition:

For non-Catholics, the Ontario system functions like a typical public system in the U.S. with a single monopoly provider.  For the 40% of children with Catholic backgrounds, however, the system is effectively a voucher program with two competing suppliers.  Although choice is limited to Catholics, the financial incentives to compete for Catholic students potentially impact the quality of schooling for all students.  Our goal is to measure the effects of these incentives using standardized student test score gains between 3rd and 6th grade.

They find that a more competitive school market, where a higher percentage of students are Catholic, leads to better performance in both Catholic and secular public schools. They estimate that if school choice was made available to all students, rather than just the Catholic students, overall performance would increase overall 6th graders standardized test scores  by 6-8% of a standard deviation. These results reinforce the idea that the impact of charter schools and voucher programs shouldn’t just compare the performance of students admitted to the programs to those that aren’t, since the main impact may be to increase test scores throughout the entire school system.