Ministers are already concerned that pupils are struggling with the move from primary to secondary school. Now they have hard evidence that children's education goes into reverse over the summer before they even get there.
This is "a significant barrier to achieving steady progress in raising standards", says a Government report, published this week.
Fifty summer schools were established to help slow readers catch up before they reached secondary school. But eagerly-awaited figures from the National Found-ation for Educational Research show that the scheme made no difference to the reading scores of the 1,500 participants.
Despite dramatic short-term gains from the three-week scheme, pupils' reading had declined by the same amount between May and September whether they attended a summer school or not.
There were, however, substantial benefits in terms of children's confidence and attitude towards books, says the report. Attendance was 95 per cent and there were no reports of disruptive behaviour.
"The Government is convinced that the summer schools provide part of the answer to supporting pupils through the transition to secondary school," says the report.
But school standards minister Stephen Byers acknowledged that the academic decline shown up in the NFER report is "a major policy issue as yet unaddressed". He said that the Office for Standards in Education will launch an investigation.
Government advisers believe that the drop in learning probably affects the summer term and holiday for all pupils, although the latest research only covers 11-year-olds.
The news adds to the debate about increasing teachers' working year to cover more of the vacation. Although expensive, this option has been urged by the chair of the Commons select committee on education, Margaret Hodge.
Ministers have been concerned about primarysecondary transfer for some time. Analyses of the national curriculum results pointed to a decline between key stage 2 and key stage 3 in 1996 and in 1997.
There were more optimistic findings from tests carried out by the summer schools. According to these, more than half the students advanced by six months or more over just three weeks.
Separate surveys carried out by the NFER and Education Extra, the group running the summer schools, showed marked improvements in children's attitudes and confidence. These benefits were carried through into the pupils' new schools.
Dr Kay Andrews, director of Education Extra, said: "The NFER findings are important and highlight a learning gap. But they don't in any way diminish the good practice or the value of progress that was made at these schools over the summer."
This year's pilot scheme was partially funded by News International, publisher of The TES and The Times. Next year the scheme will be expanded to 500 schools.