Up to 100,000 gifted pupils in England are missing out on extra help to develop their talents, an expert says.
Talented students are encouraged to attend summer schools
Sir Cyril Taylor, chairman of the Specialist Schools and Academies Trust, said 900 schools were not recommending children for government-backed courses.
The comments come as ministers launched a national register of gifted pupils to end a "terrible waste of talent".
But former chief schools inspector Chris Woodhead said grammar schools would be a better source of support.
The register follows research from education charity the Sutton Trust, which suggested just one in five children from poorer homes go on to higher education, compared with half of those from the top three social classes.
Letters sent this week to every secondary school in England will list the names of the brightest pupils identified by results from Key Stage 2 tests.
Schools will be encouraged to register eligible students with the National Academy for Gifted and Talented Youth (Nagty), which provides residential and online courses for the top 5% 11 to 19-year-olds.
Sir Cyril told the BBC: "We are really talking about a national talent search."
He said that, of the 28,000 pupils eligible for Nagty membership in each year group, 11,000 did not go on to get three A grades at A-level - the usual requirement for a place at "a good university".
Of the 3,100 secondary schools in England, 900 were not recommending bright children for extra courses, Sir Cyril added.
However, head teachers have expressed concern.
The general secretary of the Association of School and College Leaders, John Dunford, said: "One of the purposes of the register is to ensure that gifted children from poorer families are identified for extra support.
"But the existence of a list will undoubtedly lead to further pressure on head teachers from middle class parents to put their children on the register."
On Tuesday, Nagty announced its 100,000th member since it was set up in 2002, but Sir Cyril said that the figure should be 200,000 by now.
Research by an academic adviser to the Specialist Schools and Academies Trust, Professor David Jesson of York University, suggests that just 20 secondary schools are providing 10% of all England's "registered" pupils.
The Department for Education is writing to head teachers "to ensure that the background of their gifted and talented children should be broadly representative of the whole school population".
Schools Minister Lord Adonis said: "We must stop the terrible waste of talent when children don't reach their full potential.
"This register will ensure they are spotted early and don't lose out because they come from a deprived background."
Mr Woodhead, now professor of education at the University of Buckingham, told the BBC website: "If schools don't have to take part in the register then it rather undermines the whole point of it.
"But even if it were compulsory I wouldn't find it a very exciting initiative because the problem is not identifying bright children at 11.
"The problem is doing something for them and if secondary schools are not doing enough for the brightest children now why are they going to do anything for them if they are on a register?"
He added: "It is very important to try and do more for gifted children but I am afraid I do not think this is the way forward.
"If we had more grammar schools they would prosper anyway because there bright children are educated in schools for bright children."
Shadow Education Secretary David Willetts said the register was a welcome step.
He said: "To work, pupils must be taught according to their level of ability, which is why we have argued for setting in schools.
"The proposed register could be a useful tool, but we must not fall into the trap of thinking that achievement depends solely on passing ability tests. There is more to life than that."