This fact of life is used to justify banding, a system in which the test scores are segmented into a few bands, and you are then entitled to treat everyone within a particular band as essentially equal-and to hire randomly within the band.

FORBES: Quota? What's That?

Banding involves an admissions test, with results divided into ability bands - the school then accepts a percentage of pupils from each band, resulting in a mixed-ability intake.

BBC: Will reforms mean fewer school appeals?

By introduction a banding system in Wales, the government intends to group secondary and primary schools into bands reflecting their outcomes and progress.

BBC: Statement on the School Standards Unit