School support workers are being asked to work extra hours and to take classes, for little extra pay, a union has warned.
More than three quarters of those polled by the Association of Teachers and Lecturers (ATL) said they regularly work more hours than they are contracted for, with a third (33%) saying they work four or more extra hours each week.
Three in four (74.6%) of those who said they work extra hours said they do so because their workload demands it.
And more than seven in 10 (72.7%) said they do not get paid for the extra work that they do.
One cover supervisor at a Kent secondary school told the union: "In any given week I can cover up to 30 lessons plus two registrations a day. The work is exhausting. Pupils do not treat support staff with the same respect as teaching staff. We are teaching lessons, not delivering them. Our pay rate does not reflect our responsibility levels."
A teaching assistant in a primary in Warwickshire said: "I understand that budgets are tight in schools but that is no excuse for how support staff are treated. I cover teachers two days a week during which time I teach the class. The financial reward for doing this is barely noticeable in my wages"
Just over two fifths (42.8%) of the ATL members surveyed said that they cover classes, while nearly two thirds (64%) said they did not feel that the work they do as a cover supervisor is any different to that done by a supply teacher.
ATL general secretary Dr Mary Bousted, said: "It is unacceptable that so many support staff are working longer hours than they are contracted for. Even more so, they feel that they have to work longer hours because their workload demands it.
"The Government needs to address workload issues for all education staff as we know that the hours worked, and the type and impact of some of that work, is becoming too much for them, resulting in stress and illness."
:: The survey questioned 1,763 ATL members working as support staff in state-funded and academy schools in England, Wales, Northern Ireland and the Isle of Man in autumn 2015.
A Department for Education spokesman said: "We know unnecessary workload is one of the biggest frustrations for teachers and we are working with the profession to tackle its root causes, including the first biennial teacher workload survey, a commitment from the Workload Challenge.
"We want to see the teaching unions spend more time working with their members and the profession to resolve these issues.
"We trust heads, governors and academy trusts to plan their staffing. Support staff are best used when they add value to what teachers do, not when they replace them."