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Three-tier education refers to those structures of schooling, which exist in some parts of England, where pupils are taught in three distinct school types. A similar system was trialled in Scotland.
In a three-tier authorities children begin their compulsory education in a first school. Sometimes also called a "lower school" (or more simply, primary school), these schools cater for children aged up to an age between 8 and 10, and cover all of Key Stage 1 and the first years of Key Stage 2. Children then transfer to a Middle school. These schools cater for children during a period of 3 to 4 years between the ages of 8 and 14, depending on the local authority. These years cover parts of both Key Stage 2 and Key Stage 3. Following this, children transfer to a high school, sometimes known as an "upper school" for the remainder of their compulsory education, and sometimes on into the sixth form.
Many local authorities trialled systems as this for a period from as early as 1968, with many more following suit during the early 1970s, particularly in 1972 when the raising of school leaving age in England and Wales from 15 to 16 saw many secondary schools lacking the adequate class space for 11- to 16-year-olds.  However, most have since reverted to align their schools to the National Curriculum.
Some LEAs reverted to the traditional age ranges as long ago as the late 1970s. One of the first areas to revert to the traditional age ranges was Halesowen in the West Midlands, which abandoned 5-9 first, 9-13 middle and 13-16/18 secondary schools in 1982 after just 10 years in use.
No local authorities now maintain an exclusively three-tier structure. A number of authorities have a mix of standard two-tier and three-tier provision with middle schools. Central Bedfordshire, Worcestershire and the Royal Borough of Windsor and Maidenhead (Berkshire). Leicestershire operates a three-tier system in some areas, with children moving from primary school into secondary school after year six, and then to upper school after year nine.
In 2006, it was reported that Central Bedfordshire, Northumberland and the Isle of Wight were the only LEAs still exclusively using the three-tier system. The London Borough of Harrow, the city of Oxford and the counties of Dorset, Norfolk, Suffolk and Worcestershire(look up Bromsgrove and redditch) largely used the system until the 2000s and their middle schools were either closed or converted to primary schools catering to children up to age 11.
A three-tier system also exists in Gibraltar.
Presently, the 13+ intake mostly exists in the independent sector, although some have followed their respective LEAs and adopted the 11+ intake.
The main routes through education are shown in the diagram below, with three-tier routes being shown in blue and mauve:
- Northumberland Education Action Group - campaign to retain three-tier education in Northumberland