Two-thirds of support staff work overtime at least once a week and half of them are not paid for it, according to a report.
Teaching assistants, technicians and welfare staff were most likely to be expected to work extra hours for free.
The survey of more than 2,100 support staff, commissioned by the Department for Education and Skills, found secondary support staff earned an average of Pounds 1.50 an hour more than their primary counterparts.
Pupil welfare staff, technicians and administrative staff earned the most, with rates of up to pound;15 per hour in 2004.
The deployment and impact of support staff in schoolis available from www.dfes.gov.ukresearch
