Teachers have been given evidence to the ATL union with one in five staff members claiming they were aware of pupils attempting suicide in an effort to combat stress. A quarter of those cases were of children under the age of 12.
Half of teachers believe some of their pupils have self-harmed due to stress.
The study's been revealed at the ATL union annual conference in Liverpool which started on Monday.
ATL general secretary Dr Mary Bousted, who is expected to discuss the assessment system during her keynote speech to conference on Tuesday, said: "It is horrifying that young people feel under so much pressure that many are self-harming and contemplating suicide.
"The Government bears responsibility for much of this stress, which appears to stem from a test-focused, overcrowded curriculum. ATL believes that the Government's one-size-fits-all approach to school and exams disengages and fails many students.
"ATL wants all schools to have access to trained professionals to support pupils, and an education system which motivates and engages learners, instead of one which causes many young people to feel under constant pressure."
Clive Ireson from the Association of Christian Teachers says training for teachers is one solution.
Speaking to Premier, he said: "Teachers themselves are not mental health professionals.
"They can help, and do in a pastoral way...but sometimes some of those children with higher end disorders need specialist help and in many places that's not available."
He's calling on schools to prioritise mental health support for pupils.
"It's only through experience that teachers have gained what to do because they haven't had training," he said.
"One of the issues is that because the standards agenda is so high they have little time to talk to children in that way."
A Department for Education spokesman said: "We are investing £1.5 million in peer support schemes to help children develop support networks in schools and trialling a scheme with NHS England to establish single points of contact for schools to make mental health support more joined up and readily available when it's needed.
"Tests are a key part of ensuring young people master the skills they need to reach their potential and succeed in life. But we have taken real steps to ensure they are not on a constant treadmill of revision and testing, including scrapping January modules, decoupling AS levels and removing resits from league tables."