Parents have raised concerns over a loophole in planned new rules designed to stop sex offenders working near children.
Government guidance on vetting adults to work in schools specifically exempts builders and contractors from criminal records checks.
The proposals emerged just two weeks after a builder in Newcastle was jailed for grooming a 14-year-old girl for sex while working at her school.
The guidance also said new teachers would be able to start work in the classroom before their records checks have been completed.
Margaret Morrissey, spokeswoman for the National Confederation of Parent Teacher Associations, said the draft rules potentially put children at risk.
"With builders on site, especially on a large campus, it is not possible to supervise them," she said.
"They may come into contact with the youngsters.
"They will have the ability to get to know children while on site.
"If they decide to try to meet a pupil outside then the kids will think, 'well, I know him because he has been working in school, he's not a stranger.'"
The draft guidance - which is out for consultation until October 12 - was drawn up in the wake of the sex offenders row which hit former Education Secretary Ruth Kelly earlier this year.
