Responsibility for state schools in Dorset is divided between three local education authorities: Dorset County Council, which covers the majority of the county, and Bournemouth and Poole unitary authorities. Most of the Dorset County Council area operates a two-tier comprehensive system whereby pupils attend a primary school before completing their education at secondary school but Corfe Mullen, Dorchester, Ferndown and West Moors maintain a three-tier system (first, middle and high school). Bournemouth operates a two-tier system; Poole operates two and three-tier systems. Poole and Bournemouth are two of a minority of local authorities in England to maintain selective education, each containing two single-sex grammar schools which select pupils on the basis of an eleven-plus examination. Some of the county's schools are academies—self-governing state schools which have become independent of their local education authority and are maintained directly by the Department for Education. In 2017, the Progress 8 score for schools in the county council area was ranked below average, and 39.6% of pupils gained at least Grade 5 or above in English and maths GCSEs matching the national average of 39.6%. Poole recorded an above average Progress 8 score and 54% of pupils achieved Grade 5 or above in English and maths GCSEs. Bournemouth was ranked as average and 47.8% of pupils achieved Grade 5 or above in English and maths GCSEs.