But they appear to have helped move it "up-market", dispelling the low-status image which youth training inherited from unemployment schemes, according to researchers at the University of Edinburgh Centre for Educational Sociology.
"However, they may have done so partly at the expense of school-leavers with no GCSE grades - about one in 10 early leavers," say the authors of the research report, commissioned by the Department for Education and Employment.
The take-up of credits in the first 10 pilot areas was substantial, with 70 per cent of young people in jobs or schemes using them. But the take-up of training was no different outside the pilots.
Those on the pilot youth credit schemes did appear to be more discriminating. Credits increased the proportion of young people who combined training with employment, rather than opting for "trainee status" within a company.
Early fears that credits would increase the numbers of jobless school-leavers, diverting cash from the unemployed, also appear groundless. Four out of five early school-leavers in the pilot areas were employed.
"Youth credits did not increase the quantity of training, but they encouraged a shift towards employment-based and government-supported training, and they may have increased the attainment of qualifications," says the report.
But if these trends are to be sustained, the quality of vocational qualifications must be improved and training must be tailored to suit the long-term interests of individuals, as well as the short-term interests of enterprise, they conclude.