So, you’ve landed that perfect job. The school seems well run, the kids look human and the extra money will be more than useful. The only trouble is the head wants you to start at the beginning of next term and you’ve missed the deadline for resigning from your present job.

In the past teachers with good reasons for wanting to leave at short notice found that headteachers were often quite flexible about accepting resignations after the official cut-off date. But the difficulty of replacing staff in many parts of the country means that schools are now more likely to insist on teachers serving their full period of notice.

“It’s a cyclical thing. When there are teacher shortages heads are likely to interpret this requirement more stringently,” says Tim Harrison, East London regional secretary for the National Union of Teachers. “At the moment quite a lot of members will come to us and say they don’t want to stay. We have to say: ‘It is something you signed up for at the outset.’ ” Of course, there is nothing a school can do to stop you just walking out without giving any notice at all. But taking such an extreme step won’t do much for your reputation and future career prospects, either in your existing local authority or possibly even further afield. In theory a school that’s been left in the lurch could also take legal action against you, although this is very unlikely to happen.

“Pursuing a person for breach of contract is a lengthy and expensive business so, in all practical terms, there’s not a huge amount of comeback,” says Maureen Cooper, a director of the education personnel consultancy EPM Limited. For the most part, teachers act honourably and do not let their schools down, she adds. If they do walk out, it tends to be because the job is too much for them or because they have had a flaming row with their boss.

However, it’s never a good idea to resign in anger. If you have a problem - for example, with a bullying head of department or an excessive workload - there are other ways of dealing with it.

“If someone is thinking about resigning because of the circumstances of the school, they really ought to bring it to someone’s attention, get in touch with their union and use the school’s grievance procedure before taking the extremely serious step of resigning,” says Ms Cooper.

Sometimes people leave on the spur of the moment and then regret it. But if they want to retract, they need to do it very quickly, according to Olga Aikin, an employment lawyer at the Aikin Driver Partnership.

“If you resign in circumstances where someone might think you don’t mean it, which usually includes resigning in haste, then so long as when you’ve cooled down you say you didn’t mean it, you might get away with it,” she says. “But people who have resigned in writing will not get away with it because if they have actually made the effort to put it in writing, that quite clearly indicates that they did mean it.”

There is no legal requirement for anyone to resign in writing. But it would not be good practice to accept a resignation without a written confirmation of the employee’s intentions. It’s important that a letter of resignation makes those intentions clear. A letter that says, for example, “I will resign if my partner’s company relocates her” is ambiguous and won’t count as a resignation.

You don’t need to give any reasons for your resignation, although the school may find that information helpful. A small but growing number of schools now use exit interviews to find out why staff are leaving and to thank them for their contribution. Exit interviews can also be useful for the teachers themselves, as they provide a chance to receive feedback on their performance and to raise any problems that have come up during their service. These problems can escalate when teachers are serving their notice. The teacher unions sometimes receive complaints from members who believe that the only reason they haven’t gone through the pay threshold is because they have resigned. Others say that they have been given more cover lessons for absent colleagues since handing in their notice. The unions will look into such claims and, where they are justified, take steps to protect their members.

There are also cases of schools asking teachers to pay back the cost of in-service courses they have attended. This is something they shouldn’t do, unless they made it clear at the outset that teachers would have to refund training costs if they didn’t stay at the school for a certain time.

However, the NUT’s Tim Harrison stresses that these problems are the exception, not the rule. “Most heads would not in any way discriminate against someone who is resigning,” he says. “But it does happen.”

Take notice: the way to go Teachers are required to serve longer periods of notice than people in many other types of jobs. To leave a school at the end of this term, those in the state sector need to hand in their notice by the last day of February.

For summer leavers, it is May 31 and at Christmas the deadline is the last day of October. Headteachers have to give even longer periods of notice under their contracts.