Young teenagers could be at risk of "grooming" by known sex offenders taking adult education courses at colleges, a children's charity has warned.
As Ruth Kelly, the Education Secretary, sought to reassure parents about sex offenders found working in schools, the National Society for the Prevention of Cruelty to Children warned that 14 to 16-year-olds in colleges were being overlooked.
The potential for an abuser to gain access to the 93,000 under-16s in colleges needed to be addressed, the charity said.
David Coulter, education policy adviser for the NSPCC, said these students had often struggled in school, which meant they were more likely to come from violent or chaotic homes. They are also more likely to be vulnerable to abuse, he said.
"It's a real concern," he said. "They are more likely to go in for risk-taking behaviour and they don't have the support and guidance at home.
"Some FE colleges are very good at this, but they are often more loosely structured and have less good relations with social services and sexual health services. It raises some really serious issues."
Under-16s are usually taught separately but, in most colleges, they freely mix with adults in communal areas such as cafeterias and student lounges.
In one incident, an adult with a conviction for under-age sex was almost elected to a college student union post until his past was discovered.
Anyone working at a college who has contact with under-18s must have an enhanced check with the Criminal Records Bureau, which reveals convictions and other risks known to police. But those rules do not apply to adult students.
Mr Coulter accepted that it would be impractical to check the criminal record of every adult student.
But he said that good information and pastoral care could help make students aware of the danger and better equipped to ask for help.
Ms Kelly told FE Focus that the issue of protecting under-16s from adult students in colleges was considered in the 14-19 white paper.
She said: "We are looking in the white paper at separate centres in colleges for 14 to 16-year-olds where they can work in a secure environment.
"The safety and security of 14 to 16-year-olds in colleges is something we are very aware of."
Susan Pember, director of further education at the Department for Education and Skills, said it had drawn up guidelines with the Association of Colleges to help colleges protect younger teenagers.
She said the responsibility lay with governing bodies to ensure the safety of their students.
"It's for the college to determine the risk and to follow the advice of the AoC," she said. "If they have 14 to 16-year-olds on the main site, they must carry out a risk assessment. College governing bodies must be sure that they are protecting young people."
The guidance drawn up with the AoC says that schools putting pupils on a college programme should agree on supervision is necessary during breaks and lunchtimes but there is evidence of widespread concern about the potential for harm.
According to a survey by the Learning and Skills Development Agency in September last year, nearly three-quarters of colleges had some concerns about meeting their statutory child protection duties. About one in seven said they had "major" concerns.
Mick Fletcher, who carried out the research, said he had expected the concern to be even greater.
Those colleges that were unconcerned may benefit from the practice of schools which a member of staff to supervise their pupils in college, he suggested.