School vouchers have been a topic of some controversy in the past few years. Some advocate they promote freedom of choice for the families who would otherwise not be able to give their children a private education, which is supposed to provide a better educational experience, and increase competition between schools, others believe they will only increase inequalities in the access to schools and the schools that really need funding – the ones lacking means – are going to be the more impaired.
According to OECD’s Programme for International Student Assessment (PISA), school vouchers are an effective measure when given to the share of the population with the more disadvantaged students, since it decreases the inequalities in the school system (this is especially important when considering that countries with more equal school systems also have higher scores than the OECD average: “PISA 2012 also finds that the highest-performing school systems are those that allocate educational resources more equitably among advantaged and disadvantaged schools and that grant more autonomy over curricula and assessments to individual schools.” ). Yet, we should account for the possible increase in inequality between public and private schools, if there are the less disadvantage between the disadvantage that switch to private schools.
PISA’s results also suggest that, in most countries, private schools usually have more autonomy, better resources, and better PISA reading scale results than publicly managed schools . However, private schools do attract advantaged students, both because their student bodies are advantaged and disadvantaged students lack the means to join a private school – a deficit that a school voucher could suppress. PISA does imply that “once socio-economic advantage has been taken into account, the performance of public and private schools tends to be very similar” .
PISA also concludes that there is a positive relationship between school autonomy in resource allocation and students’ success, in countries where schools post their students’ achievement data publicly . Although this idea is not directly related to the school vouchers, they can be seen as a way of giving the schools more financial autonomy. This is also debatable once private institutions already benefit from that autonomy.
“Vouchers that are available for all students can help to expand the choice of schools available to parents and promote competition among schools. School vouchers that target only disadvantaged students can help improve equity in access to schools. An analysis of PISA data shows that the difference between the socio-economic profiles of publicly managed schools and privately managed schools is twice as large in education systems that use universal vouchers as in systems that use targeted vouchers.” 
Not being the only way of improving equity between disadvantaged and advantaged students, vouchers can be seen as an effective temporary measure, although the ideal scenario would be allocating all the resources in improving the public schools’ conditions in a way that equality is accomplished for all students, since recent data suggests that a well managed public education is more effective than a private one .