In the United Kingdom, a grammar school is a secondary school attended by pupils aged 11 to 18 to which entry is controlled by means of an academically selective process which sometimes consists of a written examination . After leaving a grammar school, as with any other secondary school, a student may go into further education at a college or university.

The examination was called the eleven plus. Partly due to the failure to fully implement the tri-partite system prescribed by the 1944 Education Act, the examination came to be seen as delivering a pass/fail result with the academically selected pupils passing and attending grammar schools and the remaining pupils being deemed to have failed and being consigned to the poorly funded schools euphemistically designated Secondary Modern Schools.

This arrangement proved politically unsustainable, and, over the period 1960 to 1975, non-selective ("comprehensive") education was instituted across a substantial majority of the country. The eleven plus examination had been championed by the educational psychologist Cyril Burt and the discrediting of his research amid allegations of fraud played a minor part in accelerating this process.

To understand grammar schools in the UK, some history is needed. After World War II, the government reorganised the secondary schools into two basic types. Secondary moderns were intended for children who would be going into a trade and concentrated on the basics plus practical skills; grammar schools were intended for children who would be going on to higher education and concentrated on the classics, science, etc. This system lasted until the 1960s, at which point changes in the political climate led to the general acceptance that this was a discriminatory system which was not getting the best out of all children. This was partly because some authorities tended to prioritise their budgets on the grammar schools, damaging the education prospects of children attending secondary moderns.

The decision was taken to switch to a single type of school designed to give every child a complete education. That is why this new type of school is called a comprehensive school. However the timetable of the changeover was left to the local authorities, some of whom were very resistant to the whole idea and thus dragged their feet for as long as possible. The result is that there is now a mixture. Most authorities run a proper comprehensive system, a few run essentially the old system of secondary moderns and grammar schools (except the secondary moderns are now called "comprehensives"). Some run comprehensive schools along side one or two remaining grammar schools.