During education questions in the House of Commons, Mr Blunkett said that preliminary evaluations, taken from a sample of summer school pupils, showed "substantial" improvements.

"Half of the children showed an improvement in their reading of six months or more, which is a tremendous achievement for summer schools," Mr Blunkett told MPs.

Such was the success of the scheme that there would be "at least 1,200" summer schools for 1999, Mr Blunkett promised.

Theresa May says the government is "blown off course"

As an example of how summer schools could help, Mr Blunkett pointed to the Ridings School in Halifax, which this week was removed from the government's list of failing schools.

A number of Labour members, led by Halifax MP Alice Mahon, echoed the education secretary's praise for the improvements in the school.

Summer schools offer extra lessons in literacy and numeracy to help struggling pupils to catch up before beginning secondary school.

Details of in-depth research into the effectiveness of this year's summer schools will be published next month.

While Labour MPs recounted the success of summer schools in their constituencies, a Conservative education spokeswoman, Theresa May, said that the evidence of school tests showed that the education strategy was "completely blown off course".

National test results for this year - recording a fall in standards in maths and a slowing in improvement in English - showed that the government would not reach its own targets, she said.

But Mr Blunkett replied that the government was interested in "actions rather than words" and that it had been "prepared to invest where the Conservatives only wrang their hands".