Up to a fifth of young people in deprived urban areas are dropping out of training or education as soon as they leave school at 16.
Colleges are being confronted with growing evidence of widespread disaffection among teenagers, revealing a far more serious problem in some areas than Government figures suggest.
In South Yorkshire, Barnsley College estimates the numbers of local 16 and 17-year-olds lost from the system could be as high as 20 per cent.
The pattern is being reflected in other urban areas with high unemployment. A research project focusing on the "hidden unemployed" in the Wirral, Merseyside, was launched in the light of "growing anecdotal evidence that significant numbers of 16 and 17-year-olds are falling through the net". Wirral Metropolitan College has put the figure at one in 10. However, it says the problem is potentially much worse, but is disguised by schools' tactic of maintaining drop-outs on their rolls to avoid losing funding.
Though official national figures put the proportion of drop-outs in the age group at 7 per cent, or one in 14 - much lower than local experience suggests - the Government is showing increased concern at the problem.
At a conference last week on teenage under-achievement, Education and Employment Secretary Gillian Shephard announced plans to hold a fact-finding meeting next month with college and training and enterprise council representatives and employers to seek solutions.
At the conference, Mrs Shephard stressed the need to "concentrate particularly on those young people who are currently failing to make the transition from school to employment, further education or training".
Increasing numbers of further education colleges are already working to reverse the trend, often by targeting youngsters still at school to try to spot potential drop-outs before it's too late.
Barnsley College is working with its feeder schools on a scheme designed to catch disaffected youngsters early by offering them accredited part-time courses on campus built into their school timetable. The programme, set to involve 100 teenagers this year, may also be extended to Saturdays.
For the college, the scheme represents a contribution to Barnsley's regeneration but also an investment for its own future as potential drop-outs are introduced to training and encouraged to return full-time post-16.
Because the Further Education Funding Council makes no provision for under-16s, the college dips into its own privately-earned resources to fund the scheme - a measure of its seriousness over widening provision in a competitive market.
At Wirral Metropolitan College efforts to tackle a growing local problem of 16 and 17-year-olds slipping through the training net have led to an increase in pre-16 enrolments.
The college admitted around 200 students in the age group last year, the majority through an arrangement with local schools who release pupils judged to be in danger of dropping out for a day or a morning each week.
The rest, already permanently excluded, come to college on full-time programmes offered in partnership with the pupil referral unit they attend.
Maureen Hanley, college director of studies, said: "There are a small number of students who simply respond better to an adult environment, and that is an area we need to recognise."