Cuts in funding are having a 'devastating effect' on school support staff, according to trade union Unison.
It says a survey shows spending cuts, staff restructuring and 'rocketing stress levels' are becoming the norm in UK schools.
In the report, Lessons in Austerity, almost nine in ten of the staff said cutbacks in their schools have had a noticeable effect.
More than 70% said they were carrying out duties that should be performed by someone at a higher level, and 35% that they were doing tasks without sufficient training.
More than four in five said they had experienced stress as a result of their workload in the past five years, while one in five needed to take time off sick as a result.
The union's head of education Jon Richards said: 'School support staff who haven’t already lost their jobs are buckling under intolerable workloads and mounting stress levels.
'They play a vital role in keeping children safe and schools running smoothly, they shouldn’t be seen as surplus to requirements when money is tight.'