Primary school pupils are being driven to self-harm due to anxiety caused by pressures at school and on social media, teachers have warned.
Some staff said cyberbullying and the desire to feel popular were among the most common causes of stress among their pupils.
Of the more than 400 Association of Teachers and Lecturers (ATL) members answering a survey, 81 said they were aware of pupils attempting suicide in an effort to combat stress. Of those, 18 were primary school staff.
Anecdotal evidence from ATL union members, released to coincide with its annual conference in Liverpool which started on Monday, included testimony from staff at a London academy who said: "I have seen a huge increase in physical symptoms of stress and incidents of self-harm. Suicidal thoughts have escalated beyond control."
Samantha Barlow, a mentor at a Manchester primary school, told researchers: "The Government and authorities are solely interested in levels and grades, and have put a lot of pressure on children as young as six to become anxious about exams."
A head teacher in Norfolk described mental health issues as "the biggest barrier to academic progress", while a school councillor in Warwickshire said the assessment system and time spent in front of a computer meant it was "not surprising they're getting increasingly mentally ill".
A teacher at a primary school in Somerset said: "Teachers are not social workers, psychologists or therapists, but are increasingly expected to fulfil these roles."
The research found 89% of staff polled claimed testing and exams contributed to stressed children.
Pressure to do well (70%), a fragmented home life (68%) and an overcrowded curriculum (59%) were also key contributors to negatively affecting a child's mental health, according to the study.
Pupils currently face a stream of assessments, such as the optional Baseline tests for four- and five-year-olds, as well as the Key Stage 1 and 2 exams for seven- and 11-year-olds, respectively.
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."
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."