This may involve wider social and medical issues and needs to be approached with this in mind. But first you need to rule out that it's not just happening in your classroom and the pupil is genuinely exhausted. Try to determine whether this is happening in other classes by asking around the staffroom. You can also pick up clues from pupils who may refer to the pupil falling asleep in another class.
If it seems to be a genuine problem, start by asking the pupil a few questions about why they think they're tired and be aware of how you view the problem. "Don't let the child realise you're worried, so question them calmly in a light-hearted way," says Trevor Allen, behaviour consultant at Mirror Development and Training.
"You need to give them the opportunity to open up. If you're too demanding, they will get defensive. On the other hand, you don't want to come across as overly sympathetic because they can feed off that."
Teenagers are no different from adults in the sense that many things keep them awake at night: staying up late at the weekend upsets sleeping patterns and there are endless distractions provided by the computer and TV. But teenagers may not realise the damage lack of sleep does and they may not have the parental support to guide them. There may also be the issues of overcrowding or antisocial behaviour at home, which means that your pupil can't sleep even if she wants to.
Jeff Brown, the award-winning head of Moffat Academy in Dumfries and Galloway, recommends trying to understand the pupil's social background. "Sometimes children will come up with things to fob you off, so you need to speak to their form tutor, check medical and family records and piece it together," he says.
The school should know the teenager and have information about her background. If you are worried, speak to those who deal with the pupil's welfare and if you feel it's appropriate, speak to the parents. "But you don't want them to feel like you're out to give them an argument," says Mr Brown.
Mr Allen advises caution in this situation: "You need to ask questions such as: `I just wondered what your view of this is.' Parents need to feel like they're being consulted and not blamed."
It could be that your pupil isn't eating enough to stay awake and alert, or living on an unhealthy diet. Extreme dieting causes lethargy and could be the reason behind the problem. The social education plan should cover good eating habits and you may want to ask the teacher to cover this in a lesson.
While these issues are being dealt with in the background, you still have to try and teach lessons and having someone fall asleep in class can be disruptive. Mr Allen suggests teaching your lesson plan as usual to the bulk of the class, then while they are busy, waking the pupil and giving her short tasks that don't demand too much concentration.
Ian Jamison, who teaches religion at Kingsbridge Community College in Devon, says that it's best to allow the child some time-out. "Don't try and deal with it in class - you've got up to 30 children and a lesson plan to follow. Instead, ask if they want to go to student services or whatever place the school has set up for pupils," he says.
While pupils don't appreciate individuals being singled out for preferential treatment, they're usually sympathetic. "They are quite good about cutting each other some slack and react well if someone is going through a hard time," Mr Jamison says.
Next week: Low-level disruption
. See if this is happening in other classes.
. Educate the pupil about how a healthy diet can improve their energy.
. Find out about their social background.
. Talk to parents if you feel it's appropriate.
. Deal with it in class or allow it to disrupt your lessons.
. Be placated with casual answers if you think there's something deeper going on.
. Be confrontational when talking to parents.