Schools can put up with absences of a day or two and if the quality of supply teaching is poorer than desired, no serious damage is done. But one result of an ageing and more stressed teaching population is an increase in the number of long-term illnesses, while more opportunities for secondments out of school and the popularity of childbirth, at least in our part of the world, mean that many primary classes are suddenly robbed of their teachers.

The class teacher system in primary schools is both a strength and a weakness. When everything works, there is no better place for children to spend their formative years but the reliance on one talented individual means that a vacuum in the class leadership can lead to even the best behaved of children acting as if they are auditioning for crowd parts in Lord of the Flies.

For most heads the announcement of a long-term teacher absence is accompanied by doubts about obtaining the services of an effective supply teacher. Many parents, too, recognise this problem and offer their sympathy or congratulations to the departing teacher through gritted teeth, as they foresee the uncertainty which is likely to fall on their child’s class.

Individual schools need to manage issues of teacher absence and a supply teacher deserves to find support when she takes up her post. Replacing an established and respected teacher is a daunting task when children, class routines and school policies are not known, while beyond the classroom lies a minefield of further worries about paying for the staffroom coffee, photocopying routines, car parking arrangements and locating the toilet.

A school’s initial contribution to a successful class takeover is to allocate a remit to a member of the management team to provide sufficient information, advice and encouragement during the important early days. Underestimating the time required for adjustment by teacher and children or simply closing a door and walking away will not do. Schools also need to seek the co-operation of parents.

An explanatory letter, acknowledging that a teacher’s lengthy absence can cause difficulties and including the assurance that the children will continue to make good progress should buy some time to allow the class to settle.

The supply teacher has a responsibility, too. It is reasonable to expect an air of calm confidence, an accurate idea of working levels of different ages, an understanding of basic classroom organisation and an ability to make good relations quickly with 30 unknown children. There are supply teachers who find no shame in saying: “I don’t know anything about 5-14. What will I do?”; or: “I don’t do PE.”

Such remarks are guaranteed to cast a heavy cloud over the most optimistic of head teachers. Engaging supply teachers has always been a hit-and-miss exercise and there are welcome efforts from education authorities to remove this uncertainty.

Some councils offer specially tailored in-service for returners and supply staff while others have engaged permanent supply staff from the pool of young teachers who have not found class posts.

One day, supply posts may be regarded as so vital to the health of schools that they will be occupied only by teachers who have experience and exceptional skills and whose value will be reflected in payment as a promoted member of staff.

Of course, when you have found a good supply teacher, you know what happens next. As a result of the quality experience you have provided, she does well in an interview for a permanent post in another school and you have to start all over again while parents complain about yet another change.

They really do think we have a magic wand.