The extent to which increasing students' ability to choose between schools can impact their educational outcomes continues to generate significant research interest. I take advantage of the unique context in the province of Ontario, where two publicly funded school systems operate in parallel. I find a small positive impact of school choice on student applications to university. However, most of the impact is in terms of "cross-effects"; the most robust finding is that the more Catholic high schools accessible from a neighbourhood, the better the public high schools perform. This is suggestive that one mechanism through which choice affects school outcomes is through competition between public and Catholic school boards.