Higher private school share boosts test scores.(School choice INTERNATIONAL)(Essay)

Proponents of vouchers and other measures that expand access to private schooling often claim that competition from privately operated schools will spur student achievement--and, perhaps, lower costs--in public schools. Critics of such policies, in response, note that the educational benefits of competition are unproven and that student achievement in the public sector could decline as students become segregated along lines of ability, ethnicity, or class.

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Scholars have attempted to discern the effects of competition between the public and private sectors within the United States and in other countries, but no study, to our knowledge, has attempted to measure systematically the causal impact of competition by looking at variation across countries. Until now, research has been stymied by the fact that any simplistic statistical correlations between the extent of competition and student achievement that might be found are suspect. Countries where more people choose to invest in private schools may have other attributes, such as more income or a greater commitment to education, that lead to higher levels of achievement. If this is the case, any positive correlation between private schooling and student achievement could reflect a country's income or educational commitment rather than any beneficial effects of competition. Or it may be the case that low-quality public schools increase the demand for private schooling. If so, then it could appear that competition lowered the quality of public schooling when in fact the causal connection was in the opposite direction.

In this study, we solve this conundrum by taking advantage of the historical fact that the amount of competition in education today varies from one country to another for reasons that have little to do with contemporary school quality, or national income, or commitments to education. The extent of private schooling stems in large part from the Catholic Church's decision in the 19th century to build an alternative system of education wherever they were unable to control the state-run system.

Nineteenth-century Catholic doctrine strongly opposed Catholic attendance at state-run schools that were not controlled by the Church. In the United States, for example, Catholics perceived government-operated "common schools" to be Protestant-dominated institutions that were only ostensibly nonsectarian. Local parishes responded by establishing separate schools in which children received Catholic- in fused instruction. The United States was not the only country where this happened. Catholic school systems developed in many other countries, but their size depended on the percentage of Catholics living in that country during this critical period (see sidebar). (In countries where Catholicism was the state religion, there was no perceived need for private schools, however.) As a result, even today the size of the private education sector--and thus the amount of competition between public and private schools--is related to the size of the Catholic population in 1900.

To connect the historical past to competition's effect on achievement today requires two analytic steps. We first estimate the statistical relationship between the size of the Catholic population in 1900 and the extent of private schooling today in order to capture only that share of the private sector's size that can be attributed to 19th-century Catholic policies--policies we assume to be otherwise unrelated to contemporary student achievement. Having estimated this relationship between Catholicity in the past and competition in the present, we then use that estimate to isolate the causal effect of private school competition on the achievement of individual students across 29 countries.

Our results confirm that countries with larger shares of Catholics but without an official Catholic state religion in 1900 have significantly larger shares of privately operated schools in 2003. More important, private school competition attributable to past Catholic policies generates higher student achievement in mathematics, reading, and science today. We also show that competition between the public and private sector positively affects the achievement of students attending public schools. Spending on education is also reduced, suggesting that school systems are more productive if they are more competitive.