Not so long ago, Jimmy would have made his way from the cafeteria to his seat in my classroom while chatting with his friends, as most of my teenage students do. Back then, he was regarded as a pleasant, personable young man liked by his teachers and classmates; a highly intelligent and responsible individual with spiky hair and a penchant for punk music.
But on this particular Monday, Jimmy's behaviour is quite different. He ambles over to his desk, puts his head on the table and barely moves for the next 10 minutes. He begins to whisper to another student. He does it twice, so I ask him to move to another seat, at which he smiles and in a sleepy tone responds: "Aw, Mr Robey, you used to be cool."
What happened to Jimmy? Well, he was diagnosed with depression. His parents divorced three years ago, which led to animosity and little contact with his father. On that Monday afternoon, Jimmy had been taking antidepressant medication for more than a year, but lately it had been less effective. He had missed school several times, and the previous Friday his mother had informed teachers that he had switched to a different medication. She had asked us to be alert to changes in mood or behaviour.
Depression is defined as a persistent lowered mood lasting two weeks or more. According to Harvard Medical School, as many as 8 per cent of adolescents suffer from depression in the US, with teenage girls two to three times more likely to experience it than boys. In the UK, the Mental Health Foundation says that around 10 per cent of children suffer from depression.
It is not surprising that teenagers are such a high-risk group, considering their rapid development, changing hormone levels, social, academic and parental pressures, as well as anxiety about the future. But help for these students is difficult to find. The attitude persists among many in society that depression is a weakness that can be willed away, rather than a medical condition. And when the parents of an afflicted student have this viewpoint, finding help at home can be almost impossible.
So, it often falls on teachers to intervene, but what can we do to help? Many characteristics of depression - such as low energy, weight changes and feelings of guilt and despair - can result from a variety of other causes, so correlating them with depression can be difficult. To add to the problem, many teachers have little or no training in identifying signs of mental disorders.
But although we are not qualified to diagnose depression or anxiety disorders in a student, we can look for signs. Indeed, in some cases we are best placed to spot them.
The most important thing for us to look out for is major changes in students. If a student has always been quiet, hyperactive, short tempered, mischievous or disinterested, this may just be their natural temperament. If the behaviour of a student changes temporarily, this might be down to a bad couple of days in his or her life. However, if you observe longer-lasting negative changes in mood, energy levels, interest, attention span, weight or school attendance, these should be documented and shared with the appropriate school social worker, health carer and administrative department.
But teachers need help. Depression jeopardises the learning, health, relationships and well-being of students and can, in extreme cases, lead to the risk of suicide. Therefore, training in the signs of depression should be a school matter and should be required of everyone who works with children. Until that happens, however, we need more immediate assistance.
Help comes from the American Psychiatric Association's Diagnostic Statistical Manual of Mental Disorders. It states that a person must exhibit five or more of the following symptoms over a minimum two-week period to meet the criteria for clinical depression:
Depressed mood most of the day, nearly every day.
Loss of interest or pleasure in most activities.
Significant weight loss or gain; changes in appetite.
Sleeping too much or too little nearly every day.
Feeling agitated; slowed thinking or movement that others can see.
Fatigue or low energy nearly every day.
Feelings of worthlessness or inappropriate guilt.
Loss of concentration or difficulty making decisions.
Frequent thoughts of death or suicide.
If you do notice these signs, report them to whoever is responsible for student welfare at your school. We are not psychologists and the responsibility for treatment should not be on teachers, but spotting a problem early is critical.
I know this more than most. We noticed the initial changes in Jimmy, and he sought help. When the same symptoms cropped up again that Monday, we reported it once more. In the months following, he improved with treatment and has since been doing much better. When I crossed paths with him in town recently, he was friendly and upbeat.
Jimmy was one of the lucky ones. When children's problems are not spotted, and help and support is not offered, the outcomes can be unhappy - and sometimes tragic.
Seth Robey is a science teacher from Oak Park, Illinois, US
If you have any concerns about a child, advice is available from a range of charities, including Young Minds. Find out more at www.youngminds.org.uk
How to help children with mental health issues.
Can stress at school lead to depression?
The problem with "happy pills".