Proper medical training must be given to teaching assistants who administer medicines and treatments to schoolchildren, says the public sector union Unison.
It reports that seven in 10 are expected to give medicines for conditions such as asthma and diabetes and carry out medical procedures, including changing colostomy bags.
Half are not aware that these duties are voluntary, while a third were not confident about implementing their school's policy for administering treatments.
Support and treatment that staff provide include for percutaneous endoscopic gastrostomy feeding, tracheal tube cleaning, Epi Pen use, asthma, eczema, diabetes and epilepsy.
Says Unison spokeswoman Christina McAnea: "This evidence shows a chronic lack of training and support for school staff who are expected to provide a wide range of medical support to pupils. Many reported feeling emotionally blackmailed into doing these tasks and were worried about the potential risks to children.
"Imagine the pressure of being told that a child could not go on a trip unless you would change their colostomy bag, but you hadn't had specialist training to do that job?"
Unison called for national protocols to be drawn up in consultation with education and health chiefs, as well as unions.