More than half (53%) of UK teaching assistants (TAs) have experienced physical violence at school in the past year, a poll by Unison has found.
The survey of more than 8,000 TAs found three-quarters (76%) had witnessed some form of physical violence.
More than half (53%) had experienced, and 73% had witnessed, verbal threats at school.
Ministers say no-one should have to work in fear of violence or harassment, in or outside school or online.
Unison surveyed 14,514 members who work in school support roles - such as technicians, administrative staff, caterers, cleaners, and librarians. Of these, 8,211 worked as teaching or classroom assistants.
It found that three-fifths (60%) of TAs had experienced - and 69% had witnessed - other verbal abuse at school and more than a third (38%) had experienced - 79% had witnessed - bullying at school.
Unison said its study showed that teaching assistants were facing a "barrage" of verbal threats and abuse in their job.
The full survey results of the 14,514 respondents found:
One in five (20%) had experienced physical violence at school, while more than a third (34%) had witnessed it;
A fifth (20%) had experienced (and 30% had witnessed) verbal threats at school;
More than a fifth (27%) had suffered (and 32% had witnessed) other verbal abuse at school;
Almost one in seven (15%) had experienced (and 28% had witnessed) bullying at school.
The union's head of education, Jon Richards, said the report painted a "grim picture".
"Lessons couldn't go ahead without teaching assistants and staff should not have to put up with violence and abuse in the classroom. These are not just occasional incidents.
"Abuse is becoming a regular and alarming occurrence with more than half of teaching assistants coming across violent behaviour in the classroom, the playground or at the school gates.
"A lack of resources means schools are unable to address behavioural issues.
"Dealing with these problems can dominate the day when time could be better spent supporting children's learning."
Unison called on school governors and head teachers to do more to manage the behaviour of unruly and disruptive pupils to minimise the impact in the classroom and to provide full support to staff encountering violence.
The Department for Education said Education Secretary Nicky Morgan had addressed the issue at the annual conference of the NASUWT over Easter, saying: "I want to be absolutely clear, that no teacher should ever have to work in fear of violence or harassment, either in school, outside of school, or online.
"Teachers are the pinnacle of the community, they are charged with the greatest of responsibilities, moulding the next generation, and that means we owe it to you to treat you with the greatest of respect.
"Yes, I absolutely want parents to be involved in their children's education and if they're unhappy I want them to be able to demand more of schools.
"But if their actions spill over into abuse or violence, they should expect to be dealt with severely. Because there is never an excuse to threaten, harass or attack a teacher."