More than 100 schools will drop at least 1,000 places in national GCSE league tables as ministers change how rankings are calculated, The TES can reveal.
Hundreds of others will slip down the tables as ministers toughen up secondary rankings to emphasise pupils' performance in English and maths.
Among the losers are academies, including Walsall academy and Greig City academy, north London, which are poised to fall more than 1,500 places under the new measure.
The biggest state secondary loser, Grange school, Oldham, drops more than 2,500 positions when the GCSE rankings of results from nearly 4,000 schools are changed from the old measure to the new.
At Grange, 72 per cent of pupils achieved five or more A*-Cs or vocational equivalent last summer. But the figure including maths and English was only 13 per cent, taking the school from 1,207th in the table to 3,739th.
In contrast, 228 secondaries will rise at least 500 places under the system which assesses how many pupils achieve five good passes including English and maths.
In all, 600 state schools - nearly one in five secondaries, including all 14 academies - had fewer than a quarter of pupils achieving five A*-C grade GCSEs including English and maths.
Sir Cyril Taylor, chairman of the Specialist Schools and Academies Trust, said he was raising this "shocking" figure with ministers this week. He said schools at the bottom of the new tables should be considered to become academies.
The new measure will be used in official tables from 2007, as ministers address concerns that schools have been able to claim apparently impressive results despite poor performance in core subjects.
It replaces the system which assesses the proportion of pupils achieving five GCSEs or vocational equivalent at grade C or better.
The TES compiled figures comparing secondaries' performance based on the old and new measures. The changes carry major implications for schools.
Those sliding down local tables risk losing parental support, and the funding that goes with it. Ofsted inspection judgements are being changed to stress performance in the core subjects.
English and maths teachers' associations warn that members face more pressure because of the new weight given to their subjects.
The change will also greatly reduce the impact of general national vocational qualifications on schools' rankings.
Nationally the percentage of schools achieving five good GCSEs in 2005 falls from 56 per cent under the old measure to 44 on the new one.
Waverley school, in Birmingham, listed as the most improved in England on the current measure would plunge 2,314 places in the table, its headline figures shrinking from 75 to 22 per cent.
At Greig City academy, headline results plummet from 55 per cent to 10 per cent when the measure changes. At Walsall academy, the fall is from 65 to 18 per cent.
Schools which slipped dramatically when English and maths were included have said they would not change their priorities to put more emphasis on these subjects.
However, John Dunford, general secretary of the Association of School and College Leaders, said secondaries were already changing their focus by providing booster classes in maths and English.
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