The government missed its target for participants in the National Citizen Service by more than 22,000 people, figures from the Cabinet Office show.
The department’s annual report for the year to the end of March 2015, published last week, says that 57,609 participants took part in the 2014 programme, against a target of 80,000.
The figure was also short of the minimum target of 60,000 participants set for the NCS Trust, which manages the scheme on behalf of the government.
The cost of the scheme rose from £84.2m in 2013/14 to £130.4m last year as the government began increasing the number of places available.
Third Sector reported last year that there were fewer than 40,000 participants in 2013/14, against a target of 50,000.
The latest report says that it is difficult to increase the number of participants by 50 per cent year on year "without it having a detrimental impact on the quality of the programme and the benefit to participants".
The NCS offers 16 and 17-year-old school-leavers the chance to take part in seven or eight-week projects that include community work, a physical challenge and a residential placement.
The report says that 91.3 per cent of participants completed the scheme in 2014.
A spokesman for the Cabinet Office said the 80,000 target for the NCS was an "aspirational upper estimate from mid-2013" and 65,590 places were commissioned in 2014.
Asked for details on the cost of the unfilled places, the spokesman said: "NCS Trust has a payment by results mechanism in place to combine taxpayer value with ensuring that NCS frontline delivery organisations have the cash flow they need to deliver high quality programmes. Any surpluses are handed back to the Cabinet Office."
He added: "The NCS is the fastest-growing youth movement in this country for a century. Over the past five years, almost 200,000 young people have participated in the NCS and participation in 2014 represents growth of 43 per cent compared with 2013.
"The government is committed to supporting all young people to take part in the NCS so they can gain life skills and give back to their local communities."
Nobody from the NCS Trust responded to a request for comment.
Spending on the NCS accounted for about half of the Office for Civil Society’s total spending during the year, which was £271m. The Office for Civil Society is part of the Cabinet Office.