School office workers are carrying out tasks such as administering medicines and giving first aid, according to a survey.
In some cases, these employees, working in areas such as administration and finance, are being asked to do jobs including liaising on safeguarding issues, organising criminal record checks and helping parents to fill in forms.
UNISON, which conducted the poll, said that schools would struggle to manage without school office staff.
The survey, which questioned around 1,400 UNISON members working in school office roles, found that more than half (55%) administer medicines and health support to pupils and a similar proportion (53%) perform first aid.
Nearly two-thirds 63% said they contact parents about welfare issues, while more than half (56%) help mums and dads to fill in forms, on subjects such as financial aid, and two-fifths (41%) organise checks for staff members.
And just over a third (37%) said they liaise between the school and local council on safeguarding issues.
The percentages include workers who say that these tasks are part of their job description and those who say the tasks are not part of their job, or are unsure if they are part of their job.
Almost half (47%) said there had been cuts to admin and office roles at their school in the past year.
UNISON head of education Jon Richards said: "School office staff go above and beyond every single day and schools would struggle to manage without them. If their jobs go, everyone - heads, teachers, pupils and parents - would notice the difference.
"These employees play a vital role keeping children safe, reassuring parents and ensuring the smooth and cost-effective running of schools. Without them, already overstretched teachers and teaching assistants could be pulled out of classrooms."