prior attainment or social background.

Pupils at specialist schools achieve higher GCSE grades on average than would be expected given their performance at age 11, the research reveals.

Critics of the Government’s flagship programme, who include teachers’ union leaders, have argued that the schools achieve better results because they attract more able and motivated pupils.

The research, carried out by Professor David Jesson for the Specialist Schools Trust, attempts to show the “value added” by each school based on individual pupils’ progress between 11 and 16.

It uses the 2002 GCSE results of pupils at 656 specialist and 2,342 comprehensive or secondary modern schools.

Professor Jesson said the proportion of pupils achieving five A*-C grades at GCSE was an average of 4.5 percentage points higher in specialist schools than in other non-selective comprehensives with comparable intakes.

Technology and language colleges outperformed those specialising in arts and sport, but all types did better on average than would be expected.

Pupils in the middle-ability range benefited most and schools with a high proportion of disadvantaged pupils did just as well as their counterparts in more affluent areas.

Not all specialist schools do better: 252 out of the 656 did worse than expected on the basis of their intakes. These included Bacon’s city technology college in the London borough of Southwark, one of the original CTCs set up in 1994.

There are 1,224 specialist schools, including 15 CTCs, and the Government hopes all secondaries in England will eventually become specialist.

Schools wishing to become specialist must raise pound;50,000 in private sponsorship. In return they receive a one-off capital grant of pound;125,000 and an additional pound;123 per pupil for four years.

Professor Jesson said: “This research shows substantial added performance by these schools and substantial benefits for pupils lucky enough to go them.”

But John Bangs, the National Union of Teachers’ head of education, said:

“It does not answer the criticism of a two-tier system or tackle the fact that a lot of schools miss out on the additional resources and status.”

The research by Professor Jesson, associate director for the centre for performance evaluation at York University, also suggests that the later in the school year a child is born the worse will be their results.

Both boys and girls are affected, although summer-born girls are still likely to get higher grades than autumn-born boys.

“Educational outcomes and value added by specialist schools” is available from www.specialistschoolstrust.org.uk