Bright pupils are likely to get just one chance to attend the Government's new summer schools for gifted youngsters.
The warning came as the National Academy for Gifted and Talented Youth, which runs the two and three-week residential courses, revealed it had almost filled the 900 places available this year. With more than three months to go until the courses start at six universities, including Durham and Imperial College, London, 864 places have been allocated.
This contrasts sharply with last year, when nearly two-thirds of places remained unfilled as late as the end of May and the academy was forced to appeal to private schools to fill the gap.
Fifteen thousand youngsters have now been identified by their schools as gifted and are eligible to apply for the summer schools.
A spokeswoman for Warwick university, which runs the academy, said: "Places have been filling up very fast this year. It's likely that most students will only go to the summer schools once."
Meanwhile, The TES has learnt that school budget constraints may be stopping some children from attending.
The academy's three-week summer residential courses cost pound;640 per child, with parents expected to pay pound;350 and the child's school pound;290. Michelle Stubbs said her son, Andrew, 15, and daughter, Rhianna, 12, would miss out on the "brilliant" summer schools because Campion comprehensive, in Northampton, could not find its share of the money.
Both attended the courses last year, and last month were provisionally accepted for a place.
At Campion, 30 children have applied. Headteacher Jackie Beere said that budget constraints meant that only 16 would get pound;290 each, and priority would be given to those who have not been before.
The Stubbs children have been promised pound;75 each from the school, leaving the family with a bill of pound;565 per child. Mrs Stubbs, whose husband Colin works as a supermarket department manager, said they could not afford it.
The academy runs a scholarship scheme for children from poor backgrounds, but a full rebate is only given where family income is below pound;20,000.
Mrs Stubbs said: "This makes me so cross. Children were told to apply. They did so, were given places, and then it turns out there's no funding."
Schools do not get direct funding from the academy. Cash comes from the Government's standards fund to support general provision for gifted pupils.
Ms Beere said that it cost the school pound;4,640 to send 16 pupils to the summer school. The total standards fund cash for the school is pound;18,000, which must cover gifted support throughout the year.
With limited cash, the school has to provide for as many talented pupils as possible. This year it plans to run its own summer school for the gifted.