Teaching assistants are using their own money to help cash-strapped families buy school uniforms and lunch as well as fund trips, new research suggests.
Unison said its study also indicated that schools are providing emergency supplies of groceries, with many running food banks for families.
The union said a survey of more than 4,500 teaching assistants from primary and secondary schools across the UK revealed that pressured, low-income families are turning to schools for basic support.
More than half of respondents said parents are increasingly in need of more help and reported pupils arriving at school hungry more often.
Two in five said they were witnessing increasing levels of poverty.
More than a fifth of those surveyed said they had bought uniforms or PE kits, while 20 per cent had helped pupils with lunch money.
Nearly one in five said they had provided cash so children could go on a school trip.
Unison's head of education, Jon Richards, said: "It's shocking that some parents are so desperate they're turning to teaching assistants and schools for help.
"This demonstrates that support workers are not just essential in the classroom. Their role now extends to acting as benefactors, so pupils and their families don't go without, despite many not earning much more than the struggling parents themselves.
"They go above and beyond their job descriptions day in, day out. Yet the Government fails to recognise their worth by paying them a decent wage or acknowledging their vital contribution to children's education.
"They should be getting behind teaching assistants, just as they have teachers and school leaders."