The potential of fast-tracking in raising achievement was seen at first hand by David Milliband, head of policy in Tony Blair's office, on a visit to Grove junior school in Handsworth, Birmingham, writes Geraldine Hackett.
By any measure, the Grove is an exceptional school. Dr David Winkley, head for the past 20 years, is also an influential figure in the city's education circle and director of the National Primary Trust.
The reference in Tony Blair's speech to 11-year-olds achieving GCSEs probably only applies to the Grove, where this year four 11-year-olds passed the intermediate paper in maths GCSE.
The school has a maths set of 36 pupils aged from eight to 11, doing work at least two years ahead of the national average. There are also sets for children with special writing, dance and musical ability. According to Dr Winkley, the school's success is down to the quality of teaching. The fast-track classes tend to be taught in larger groups, with children requiring special help given more individual attention.
However, while there is a move back to setting in schools, there are few other examples of secondary schools where pupils are taught in mixed-age classes. Many secondary schools set by ability in maths and science, but teach English in mixed-ability classes.
In the past, grammar schools tended to enter their top set for exams a year early, allowing such pupils to join sixth-forms at 15. Schools such as the one cited by Labour aides, The Marches in Shropshire, continue to do so.
The teaching unions are not enthusiastic about setting on the basis of ability regardless of age, but there is little recent research on its effectiveness.
David Reynolds, professor of education in Newcastle, who has been looking at education in the Pacific rim countries, suggests their success may be partly accounted for by the fact that they do not attempt to teach in one class children spanning a wide ability range.
"If we look at countries that do accelerate children, they also hold back children until they have developed the necessary skills. In that way they reduce the range of ability being taught by a particular teacher," he says.
"If you consider the range of ability among ten-year-olds and the trend to integrating children with special needs, then teachers here have to work within a complex technology of teaching.
"Exceptional teachers can always produce exceptional results, but if we are looking across all schools, a simple technology might be more effective. "
Ted Wragg, professor of education at Exeter, believes there are limits to teaching classes of mixed ages. "In theory, you could have average 11-year-olds, bright seven-year-olds and slow-learning 14-year-olds all working at the same national curriculum level," he says.
On a more practical level, he says fast tracking in the early years of secondary school is likely to occur at the stage where girls stride well ahead of boys.
The unions were quick to point to the organisational problems of fast tracking. Nigel de Gruchy, general secretary of the National Association of Schoolmasters Union of Women Teachers, said such schemes have been tried over the years by many schools. "Many schools have discontinued these experiments. They have found that they often place individual children in difficult circumstances," he says.
David Hart, general secretary of the National Association of Head Teachers, believes it is not desirable to teach bright pupils with older students.
"First, their needs can be coped with by setting pupils in academic subjects, thereby ensuring that the brightest are taught together. Second, educating pupils alongside those who are older deprives them of the opportunity of mixing with pupils of their own age," he says.
The policy has attractions for Labour in that it offers an answer to those critics of comprehensive education that claim such schools offer only uniformity and do not cater for exceptional pupils.