Criminal sanctions should not be used to force young people to stay in education until the age of 18, says a charity which works with ex-offenders.
Young people will have to stay in education or training until the age of 18
Nacro says the case for requiring teenagers to stay in education had not been proved - and warned of further "criminalising" disaffected youngsters.
For many disengaged youngsters "continuing for a further two years under duress" is not right, it said.
Ministers have claimed enforcement measures would only be a last resort.
The Department for Education and Skills (DfES) announced in January that by 2015 all young people would be required to stay in school, education or training until the age of 18.
Recent figures for England showed that 11% of 16 to 18-year-olds are still outside education, training or work.
Making this compulsory, with the threat of sanctions, has been challenged by Nacro (the National Association for the Care and Resettlement of Offenders).
Nacro's director of operations Claire Bassett said the aim of widening participation in education was welcome, but that the case for compulsion had not been proved.
"We would like to see the positive measures, such as a broader range of educational provision, comprehensive information, advice and guidance services, and increased support for young people at risk of dropping out, introduced without the element of compulsion.
"The success of these proposals is dependent on a huge shift in the scale and type of education provision and related services, which is an ambitious task. But without this many young people will be set up to fail."
She added: "We are also extremely concerned about the possibility of severe sanctions for those who find continued participation impossible.
"Using criminal sanctions will provide yet another way for disadvantaged young people to criminalise themselves."
The charity will be urging the government to rethink its proposal when it makes its submission to the consultation on the plans which closes on Tuesday 12 June.
It comes after the academics union the University and College Union backed a motion at its annual conference, opposing government plans to raise the school leaving age.
Both the Conservatives and the Liberal Democrats believe compulsion and threats are the wrong approach to increasing participation.
A spokesperson for the DfES said the proposals were not about "forcing young people to do something they don't want to".
There would be a range of options for young people - including school, college, work-based learning or accredited training with an employer, said the DfES.
"We are letting young people down if we allow them to leave education and training without skills at the age of 16," said a DfES spokesperson.
"If young people drop out they will be supported to re-engage through integrated Youth Support Services, offered alternative learning options and local authorities will explain their duty and the consequence of not participating.
"At this stage, it is proposed that they will be issued with an attendance order. We are consulting on this model of enforcement and we welcome views on this."