A comprehensive school is a secondary school that is a state school and does not select its intake on the basis of academic achievement or aptitude. This is in contrast to the selective school system, where admission is restricted on the basis of selection criteria. The term is commonly used in relation to England and Wales, where comprehensive schools were introduced on an experimental basis in the 1940s and became more widespread from 1965. About 90% of British secondary school pupils now attend comprehensive schools. They correspond broadly to the public high school in the United States and Canada and to the German Gesamtschule.
Comprehensive schools are primarily about providing an entitlement curriculum to all children, without selection whether due to financial considerations or attainment. A consequence of that is a wider ranging curriculum, including practical subjects such as design and technology and vocational learning, which were less common or non-existent in grammar schools. Providing post-16 education cost-effectively becomes more challenging for smaller comprehensive schools, because of the number of courses needed to cover a broader curriculum with comparatively fewer students. This is why schools have tended to get larger and also why many local authorities have organised secondary education into 11–16 schools, with the post-16 provision provided by sixth form colleges and further education colleges. Comprehensive schools do not select their intake on the basis of academic achievement or aptitude, but there are demographic reasons why the attainment profiles of different schools vary considerably. In addition, government initiatives such as the City Technology Colleges and Specialist schools programmes have made the comprehensive ideal less certain.
In these schools children could be selected on the basis of curriculum aptitude related to the school's specialism even though the schools do take quotas from each quartile of the attainment range to ensure they were not selective by attainment. A problem with this is whether the quotas should be taken from a normal distribution or from the specific distribution of attainment in the immediate catchment area. In the selective school system, which survives in several parts of the United Kingdom, admission is dependent on selection criteria, most commonly a cognitive test or tests. Although comprehensive schools were introduced to England and Wales in 1965, there are 164 selective grammar schools that are still in operation. (though this is a small number compared to approximately 3500 state secondary schools in England). Most comprehensives are secondary schools for children between the ages of 11 to 16, but in a few areas there are comprehensive middle schools, and in some places the secondary level is divided into two, for students aged 11 to 14 and those aged 14 to 18, roughly corresponding to the US middle school (or junior high school) and high school, respectively. With the advent of key stages in the National Curriculum some local authorities reverted from the Middle School system to 11–16 and 11–18 schools so that the transition between schools corresponds to the end of one key stage and the start of another.