By Alison Smith
BBC News education reporter
Kids can be cruel - we all remember.
Educationists say more children are suffering than ever
But if you suffer from mental illness, what starts as a teenage taunt of "weird" or "nuts" can turn into discrimination and bullying.
Samantha Hilton remembers her friends literally walking away from her. She had started self-harming because of depression from the age of 13.
School was "hell" she says - a catalogue of rejection by teachers, friends and doctors, who put her behaviour down to "teenage angst" or hormonal changes.
Her account does not shock PhD student Emma Lindley, who has devised lessons to help teachers combat the stigma surrounding mental illness in children.
She researched a method to make children think about what mental illness really means and their reactions to it - because they are fairly likely to encounter it at some stage in their lives.
Her research and instinct told her that if children could understand the reasons behind a fellow pupil's strange behaviour, they would be less likely to treat them badly.
But to what extent should schools intervene - or teach about mental illness at all?
Educationists such as Sir Mike Tomlinson say the number of children suffering mental health problems has risen greatly over the last 10 years.
The Department of Health says the number of children and adolescents using mental health services is 160,313. It acknowledges that there was a 31% caseload increase between 2003 and 2005.
There is no statutory requirement to teach about mental illness - though it can be brought into personal, social and health education (PSHE).
Samantha says her teachers were interested in her situation only in so far as it affected her behaviour or work.
She faced the double difficulty of dealing with both the illness and the trauma of isolation at school.
Her friends saw someone who became withdrawn and unsociable, saw the marks on her arms and legs, and shunned her.
"I'm sure they didn't understand my behaviour," she said. "But nobody spoke to me about it. Not even the teachers."
Now 22, she was put off going to college, and works for the mental health charity Mind.
Emma Lindley took her research ideas to a group of 14-year-olds in south Manchester, showing them photo vignettes of people displaying strange behaviour, with accompanying case histories.
The idea was to get behind the medical labels and encourage them to empathise.
The results have just been published in the International Journal of Mental Health Promotion.
"The children told me they wished they'd had a chance to talk about this in school before," she said.
"Most did have some prior experience of someone with a mental health problem."
This was no surprise to Emma, since one in four of us is likely to experience some form of mental illness.
But she had a shock for the children when she told them that during an episode of bipolar disorder in her early 20s, she had believed she was a spy with a mission to bring down the Queen.
The children struggled to reconcile this with the articulate and normal-behaving PhD researcher before them.
"They couldn't believe it," Emma said.
Emma Lindley's research is for the University of Manchester
"Then they started to understand that the issue of mental illness is a complicated thing.
"It's not like racism or sexism where your status doesn't change."
Emma says that it is not as simple as trying to eliminate prejudice, as during an episode of mental illness, it may actually be appropriate to treat somebody differently.
Teenagers may not yet have fully learned how to empathise with those who are different - but being different is not always the issue.
The Department for Health's Attitudes to Mental Health survey from 2008 said fewer people than in the past said they thought it was easier to tell someone with a mental health problem from an "ordinary" person.
Recent research suggests teachers are well placed to help children deal with those suffering mental distress.
Where stigma becomes bullying, they must intervene - but they increasingly recognise that a change in attitude among children themselves is required.
The mental health campaign group Time To Change surveyed more than 3,000 adults living with mental health problems - and a majority thought education to prevent negative attitudes should start in school.
Nine out of 10 respondents said stigma had a negative effect on their lives.
The organisation now runs workshops to train teachers to recognise the signs of mental illness and combat such stigma.
Emma Lindley believes lives can be changed by starting early.
"Educators have the potential to make a real difference to those who are suffering from mental distress," she said.
Last year the government launched a more targeted form of support for children with mental health problems, involving direct links between primary care trusts and schools, to help children displaying signs of mental illness.
Teachers who Emma spoke to told her mental illness was a real taboo in schools - even though it is not uncommon in the profession itself.
In lessons, they may resort to a quick reference to a storyline in popular teen soap Hollyoaks, bringing it into PSHE.
But what both Emma and Samantha say is that children need to be taught about real scenarios - which could happen to any child, in any school.