The Government is going ahead with a pound;13 million programme involving 900 schools and 27,000 pupils - up from 558 schools and 16,000 pupils last year.
This is despite an evaluation of the 1998 scheme which showed that 45 per cent of the 16,000 pupils went backwards between the start and end of the three-week programmes. A total of 47 per cent of children made small gains.
However, there was better news for the Government in respect of maths. Three quarters of the pupils involved in pilot numeracy schools managed to improve their results, with nearly 5 per cent seeing gains of 10 or more marks.
Overall, mean test scores rose from 13.3 to 17.3. Pupils started with a wide range of abilities -rated from below level 2 to level 5 of the national curriculum - but all improved equally.
The 1998 literacy findings echo an evaluation carried out on pupils involved in the first summer schools, in 1997. That compared pupils test results in May and September - rather than at the beginning and end of programmes -and found no difference between those pupils attending summer schools and those not.
However, both evaluations show the schemes boosted children's confidence and encouraged more positive attitudes.
Education Secretary David Blunkett defended the summer schools, saying they were helping to address the problem of summer learning loss and the difficult transition from primary to secondary education.
"What the summer schools are intended to do is to increase the confidence of children who fell behind in their reading during primary school, in advance of starting at secondary school. The evaluation found that they were achieving this objective," he said.
"We introduced the summer schools because too many youngsters had not had the benefit of the recently-introduced daily literacy hour. Secondary teachers were having to provide remedial lessons rather than concentrating on the secondary curriculum. Nobody would expect dramatic changes in scores in 15 days, after six years of falling behind."
He promised new, "sharply focused" teaching guidance for literacy summer schools, which will emphasise phonics, spelling and grammar.