One of the reasons that decisions to open new selective schools should not be devolved to local decision-makers is that it affects pupils and schools in other local authorities. This is because families are able to seek a school for their child in a different local authority to the one they live in, thanks to the 1989 Greenwich Judgement. About 1-in-5 pupils at grammar schools cross local authority boundaries each day.

This means that ‘grammar school areas’, defined as local authorities with selective schools, and ‘grammar school areas’, defined as areas where pupils attend a grammar school, can be two very different things. The map below highlights the local authorities containing one or more of the 163 remaining grammar schools today. The deeper the blue, the greater the proportion of secondary schools that are selective.

grammar_contamination_LAonly

This second map plots the proportion of pupils in an area attending a grammar school. (Here we pool the last five years of age 11 entry to grammar schools for each middle super output area.) The spillover of, for example, the Kent grammars into East Sussex and the Lincolnshire grammars into Nottinghamshire and Leicestershire becomes apparent.

grammar_contamination_spillovers

The Trafford grammar schools serve a very wide area of Manchester, Stockport, Warrington and east Cheshire. Indeed, some areas of Trafford itself rarely send a single child to the grammar schools.

grammar_contamination_spillovers3

The decision to retain a handful of grammar schools in Bournemouth, Poole and Wilshire has affected the provision of all-ability comprehensive schooling in east Dorset and west Hampshire.

grammar_contamination_spillovers4

It is reasonable to describe the whole of south London, except for Southwark and Lambeth, as a selective schooling system since significant numbers of the highest attaining pupils are migrating to grammar schools. The opening of a new grammar school annex at Sevenoaks, within walking distance of mainline stations, is likely to increase these flows.

grammar_contamination_spillovers2

So, grammar schools contaminate areas where politicians had decided to implement comprehensive schooling reforms. As a result, comprehensive schools in non-selective areas find they are not truly comprehensive since they have far fewer high attaining pupils. They experience similar difficulties to secondary moderns in appealing to middle class parents (since their raw exam results are depressed) and recruiting suitably qualified teachers.