GRAMMAR schools produce less improvement in pupils than comprehensives, new research claims.
The study measures the progress made by more than 500,000 pupils in the two years between key stage 3 and GCSE. It suggests that schools in selective areas are significantly worse at "adding value" than their comprehensive counterparts.
None of the 15 authorities with large numbers of grammars was in the top 10 value-added authorities. Four were in the bottom 10.
The findings by Professor David Jesson of York University, a government adviser on league tables, will be seized upon by campaigners for abolition of the country's 164 grammar schools.
Last year the professor produced controversial data questioning whether grammar schools really helped gifted children.
At that time he also claimed that the Government could raise the proportion of pupils gaining five good passes at GCE by three percentage points, simply by ending selection.
He said his latest results, presented a the National Union of Teachers' secondary education conference this week, would make for sober reading among those who champion selection.
"None of the evidence ... supports the claims that have often been made that 'selective education provides best educational performance'," he said.
In his study, Professor Jesson uses a framework developed by the Office for Standards in Education to compare the performance of different schools.
More than half the grammars are in the lowest two categories out of seven compared to 41 per cent of comprehensives. Only 13 per cent of grammar schools are in the top two categories compared with 17 per cent of comprehensives.
Grammar schools are concentrated in just 36 of the 150 English education authorities. Authorities with large numbers of grammars include: Bexley, Bournemouth, Buckinghamshire, Kent, Kingston-upon-Thames, Lincolnshire, Poole, Reading, Rochester, Gillingham, Slough, Southend, Sutton, Torbay, Trafford and Wirral.