If you have ever worked in an office, you'll know that the occasional absence to see a doctor, dentist or sort out some personal matter is not considered unreasonable. Not so in schools. Many teachers feel so guilty about letting down colleagues and students that they refuse to take time off. And that means they neglect their health in the process.
"I always try to make appointments outside school time if I possibly can," says Louisa Kelly, who teaches maths in a secondary school in Northampton.
"It's just not worth the hassle. You see the frowns on colleagues' faces as they check the cover board and see they're having to take your lesson.
They're so irritated that they just get on with their own work and couldn't care less whether your students learn anything in the lesson. You get back to school and you often have to repeat the work."
It may be inconvenient but a slot with a doctor or dentist can usually be arranged out of school time. But hospital appointments can be more awkward.
Tom Clayton had suffered back problems for some years before he was referred to a consultant, who prescribed a course of intensive physiotherapy. The treatment was offered on the NHS, but when he realised what impact the weekly visits would have on his job, he paid for private treatment out of school hours.
"It just wasn't worth it," says the primary teacher from north London. "I couldn't let the pupils down, and I don't think my head would have been too pleased at the cost of cover, either."
But sometimes events are totally beyond teachers' control.
When Miss Kelly's grandmother died last year, she expected to attend the funeral without question. Yet she was quizzed at length by her deputy about why she wanted to attend.
"She didn't say it outright, but I felt she was challenging my need to be there," she recalls. "I know some people aren't close to their grandparents - but I was, and it was important for me to be there. There are no hard and fast rules about relationships. Some people are closer to friends than family, for example. Where funerals are concerned, this has to be respected."
Local authorities often have leave of absence procedures, which have been set up in consultation with teachers' unions. Schools are encouraged to adopt these arrangements - which vary from one authority to another - and most do.
The arrangements give details of the recommended time off for a range of activities. They include funerals (usually of close relatives), carer leave, house moves, medical appointments (including ante-natal appointments) and interviews. But attitudes vary from school to school, says Chris Keates, general secretary of NASUWT, the second largest teaching union.
"Most are reasonable and recognise that individuals have little control of hospital appointments, the death of close relatives, emergency medical treatment or interviews for jobs," she says.
"Unbelievably, however, some do not - and we have considerable casework experience of heads and governors refusing time off for family funerals, illness of a child, interviews and, in some cases, hospital appointments.
Time has been refused or pay has been docked."
Problems are most likely to arise around events over which heads believe their staff have some degree of control, such as routine medical or dental appointments and house moves.
"The major problem is that most leave of absence is at the discretion of the employer," says Ms Keates. "This leads to a variation in interpretation - even where a local authority scheme has been agreed - and in some cases to unfair and discriminatory practice."
Tom Lewis, director of operations at the Teacher Support Network, believes teachers should not be apologetic about requesting time off for personal commitments. They should, though, think carefully about how they make the request. "First, make sure you're informed about leave-of-absence policies - in your school and LEA," he says.
"That should put you in a stronger position. If you need to ask your head or other senior member of staff, don't just try to catch them in the corridor. Ask to speak to them when they're not too busy. And give them lots of notice so they have time to plan ahead.
"If you can come up with a solution - arrange cover with a colleague, for example - even better. If necessary, offer to take time off as unpaid leave. Most headteachers won't resort to this unless it's strictly necessary, and it will show that you're willing to be reasonable."
If you do believe you are being unfairly refused time off, Ms Keates says you should ask to see the school or local education authority policy on leave of absence, then take advice from your union. In the long term, she hopes to see improvements in procedures.
"The answer is a nationally agreed entitlement so that employers and employees know exactly where they stand," she says.