As far as embarrassing situations are concerned, this comes somewhere between uncontrollable flatulence and the boy who can't stop "adjusting" himself. But it could also have potentially serious consequences for the pupil concerned, leaving him socially isolated, with resulting social and emotional - leading on to behavioural - problems.
And however embarrassing it is, in these days of Every Child Matters, ignoring it is not an option. "If a teacher is aware of this kind of situation, where there are some health and social and emotional issues at play, they have got a responsibility to be proactive," says Kairen Cullen, an educational psychologist.
One option is to suggest a visit to the school nurse. Although body odour is unlikely to be the result of a health problem in a teenager - more commonly linked with the menopause, diabetes or kidney and liver disease - dressing it up as a health issue may make it easier for the boy to accept.
If this doesn't work, and hints aren't getting through, then the direct approach may be the best route. But brace yourself for an awkward encounter.
"You don't just suddenly start a conversation like that," Ms Cullen says. "You have to have an open and trusting relationship with the young person, otherwise it could be excruciatingly embarrassing and they could react so emotionally they don't hear the message."
If you don't have that sort of relationship with the boy, then one option would be to work through their form tutor or favourite teacher. And when you do get into position to have this conversation, then honesty, with a heavy dose of sensitivity, is the best policy. One gambit might be to normalise it, talking about how lots of young people experience a surge of hormonal activity. It shouldn't take too long for the penny to drop. "Young people are not stupid," says Ms Cullen.
David Miller, a teacher at St Ninian's High School in Glasgow and Secondary Teacher of the Year at last year's Teaching Awards, agrees that pussyfooting around the subject is unlikely to get results. Nor should you overdo the emoting.
"If you're going to tackle a thing like this it would need to be with absolute candour," he says. "You have to do it with complete equanimity." Mr Miller's approach would also relate it to normal changes in an adolescent boy, avoiding making them feel what is happening to them is exceptional.
Body odour can be exacerbated by obesity or eating spicy foods, but it could also mask other issues. The boy may have low self-esteem or problems in his home life, perhaps a lack of parental support or no proper washing facilities. To get to the bottom of these, it is important that he knows you care about him. "The child needs to know that it is his welfare that is important to you and not the ignorance of the other insensitive pupils," says Alan Haigh, author of The Art of Teaching.
The conversation may be the result of a personal hygiene issue, but it should be with the pupil, rather than to him, and inquiring about his feelings and wellbeing. "The social and emotional aspects of his life are most probably at a low ebb and any praise and encouragement you can give him will help," says Mr Haigh. Tiny steps of kindness will help build his confidence and trust in you. "When this is established, you will find he will respond to quiet advice," he adds.
- Next week: Mobile phones in class
. Take a direct but sensitive approach. Skirting around the issue only prolongs the embarrassment.
. Talk about it as a normal part of growing up so they don't feel they're the only ones in this situation.
. Make some practical suggestions, such as using deodorant, washing regularly or washing their clothes.
. Think about involving other professionals, such as social workers or educational psychologists, if you think there are deeper issues involved.
. Ignore it. You have a responsibility to promote your pupils' emotional health.