For a few people supply teaching is an ideal way of life, allowing them to juggle work, family and friends in a much more creative and flexible way than 9 to 5 employment allows. For others it is an experience so unpleasant that it ends their teaching career before it has properly begun.
For most it is a rite of passage, an intense learning period, a part of their career that is usually stressful, sometimes fun, occasionally frightening, but - best of all - only temporary.
But sometimes temporary can last so long it feels like permanent without the holiday pay. "After working in industry for 20 years I did a PGCE in maths," says Edward Maxwell, "hoping it would be fairly straightforward to get a permanent job. It took me three years. And in that time I taught every subject you can think of - home economics, geography, PE, English. Oh - and a bit of maths as well."
Short-term supply is perhaps as difficult as teaching gets, with maybe two or three different schools in a week, and five classes a day in secondary schools, each one at first a sea of nameless faces. Gaining and keeping control of as many as 30 lively young strangers is the problem most often mentioned.
"I qualified in the 1970s," says English teacher James Blake, currently at St Thomas Aquinas Secondary in Glasgow, "and supply teaching suited me. It was flexible and meant I could stay at home if my wife was busy to look after the kids. But in the early days I had some torrid times.
"You're going into situations where the kids are thinking 'I'm going to take the mickey out of this guy', so within the first couple of minutes you have to stamp your authority on the class."
From the supply teachers' point of view, it is unfortunate that every school has its own disciplinary procedures - ideally these would be uniform across an authority or even the whole country, making one less item to be absorbed in the 20 minutes between arrival at a new school and the first bell.
Schools, say supply teachers, could smooth their path greatly by always providing two essential sets of paperwork - a brief description of the school disciplinary procedures, complete with all necessary forms, and a seating plan for every class to be taught.
"You try to avoid shouting 'You boy, be quiet'," says technical teacher Andrew Hill, currently on supply at Knightswood Secondary. "But sometimes you have to. It makes the job so much easier if you know their names."
"I had a terrible time in one school," says physics teacher Bill Johnstone (not his real name), "where the assistant head arrived at two minutes to nine, gave me a school handbook and a list of classes to teach and told me to get on with it.
"I found out later that discipline was based on punishment exercises, but they're completely useless if you're in a school for just a day or two. Later that week I taught at another school - Bannerman High in the east end of Glasgow - where they had a well-structured system of demerit and praise slips with graduated punishments and rewards. It seemed to work really well because the threat of the lowest level demerit was usually enough to calm the kids down."
But classroom control is not just a matter of being strict and knowing names and procedures. Communication is a two-way process, and while a class is sizing up a new supply teacher, he or she should also be assessing them.
"I do a bit of beekeeping in my spare time," says Mr Johnstone, "and as soon as you open a hive you can tell what mood the bees are in. If they're upset or fractious you have to be alert or you'll get badly stung. Other days they're contented and you can relax a bit.
"Classes are like that, and you need to learn to respond to their moods. Sometimes being hard is appropriate; sometimes it isn't. It's the easiest thing in the world to turn a class that began a lesson in good humour unco-operative and surly by picking on every little thing they do."
With younger children this is even more apparent, because some of them are likely to burst into tears if teacher is too severe.
"You do have to be firm though, even with the wee ones," says Zahida Din who completed a BEd degree this year and is supply teaching at Albert Primary School, Springburn.
"I teach the Primary 1s every morning and at first it's a matter of getting them into a routine - putting things away, sitting quietly, listening to the teacher.
"When they go home at lunchtime I have please-takes in the afternoon, so I've taught just about every class in the school. I try to gauge the way their usual teacher handles them by how they react and answer my questions. You soon find out what works."
Outside the classroom the practical difficulties associated with short-term supply teaching, such as trying to raise a mortgage without a permanent contract, are perhaps not as great as they once were.
"I thought it would be difficult getting a mortgage or a loan," says Andrew Hill, "but I've just re-mortgaged my house without any trouble. More and more people are on temporary contracts these days, so I guess the banks have to do something about it."
Local authority support Local authorities too have begun to recognise that supply teachers need support and encouragement and are not simply a collection of hardy souls who can be left to fend for themselves.
Partly, say the authorities, this is motivated by a desire to improve working conditions for all their employees; partly it is a result of increasing problems countrywide in providing supply cover to schools - and partly it is a response to the McCrone committee, which described the situation of probationary teachers given little help or guidance and "teaching in a multiplicity of schools on a supply basis" as "little short of scandalous".
The problems of probationers and supply teachers do overlap because "more often than not these days a new supply teacher arriving at a school will be a probationer," says Iain MacDonald, primary adviser with Glasgow City Council.
"There are simply fewer experienced teachers around who are happy to do it. In Glasgow we are trying to help supply teachers in a number of ways, by organising and running courses and by developing useful materials."
Margaret Lynagh, currently at Our Lady of the Assumption Primary School, attended Glasgow's induction course this summer: "It lasted a week just before the schools went back, and although we'd done some of the topics at college it helped to jog your memory - it's a long summer break - and we got a lot of practical tips about report-writing, dealing with parents, and so on from experienced teachers."
Glasgow also produces an information pack and runs a twilight programme of classes from September to March, open to all supply teachers and probationers, and covering a range of topics from effective teaching and early intervention to child protection and promoting positive behaviour. Times, dates and application forms are distributed to headteachers and staff development co-ordinators in schools who should get the information to their supply teachers.
The education deparment is currently developing the Glasgow Educational Network, a website for teachers and schools. "We think it will be very powerful," says George Gardner, depute director of education.
"One of its features will be a virtual staffroom where any teacher can access information about what's available and what help they can get from us. There will also be distance learning material, so if they are unable to go to one of Mr MacDonald's courses, they can download the text, and in time should even be able to do the course at home via the Internet."
A number of authorities have recently created pools of supply teachers who are employed on permanent, full-time contracts. But as yet these pools exist only in the primary sector and are relatively small even in large authorities - 30 teachers in Glasgow and 17 in Edinburgh - so are likely to have little impact on the average supply teacher.
Glasgow, for example, can currently call on 1,109 primary and 1,760 secondary supply teachers, while Edinburgh has a total of 754. In fact, filling long-term supply posts preferentially from the pool might render the experience of the remainder even more fractured and unpredictable.
There are no simple solutions to the problems of organising teachers to meet the sometimes incompatible needs of schools which require cover and teachers who want a career - full employment for every supply teacher would mean no one was available at short notice. But local authorities are beginning to recognise that schools as well as supply teachers benefit when the latter are given as much support and training as those on permanent contracts.
Supply teaching is a demanding and stressful way to earn a living but it is also highly educational - for the teachers, if perhaps not always for the children.
"Sir you've taken us for music and maths already today," one boy told Mr Johnstone, "and yesterday you had us for PE. What subject is it you teach anyway? And how come you still don't know my name?"
VIEWS OF SUPPLY TEACHERS
* Zahida Din primary teacher
"Don't believe everything you hear. My friends were really concerned when I said I was going to a school in the east end of Glasgow, but I've found the kids here mostly well-behaved and with a good attitude to work."
* James Blake English teacher, secondary
"Supply teaching certainly gets your discipline skills organised, and in the early days you've got to expect some difficult times. Once schools get to know you they begin to ask for you by name, and a day here and there soon becomes a couple of weeks or a month."
* Andrew Hill technical teacher, secondary
"Supply teaching gets less stressful once you accept you're not going to get a permanent job right away and this is how you're going to have to live for a while. Also, don't feel embarrassed about phoning up every day and asking for work - I've only missed 13 days out of the last two years."
* Bill Johnstone physics teacher, secondary
"At the moment supply teaching is a seller's market, so if you don't like one school you should easily find work in another one, especially if you put your name down for general supply and not just your own subject."
* Margaret Lynagh primary teacher
"Don't be afraid to ask other teachers for help. A lot of schools have mentors now whose job is to help inexperienced teachers, and I've generally found most of the staff in schools very approachable."George Gardner depute director of education at Glasgow City Council "Supply teachers should always keep in touch with their local authority, which should be able to provide them with any training and staff development they feel they need.
* George Gardner, depute director of education at Glasgow City Council
"Supply teachers should always keep in touch with their local authority, which should be able to provide them with any training and staff development they feel they need.
* TALES FROM AROUND THE COUNTRY
"At the start I put my name down for general supply because I wanted as much work as I could get. One morning I had a second year home economics class and they were a bit annoyed because I couldn't teach them sewing, but eventually I got them settled down. Then the head came in and ushered a wee boy to a seat at the front.'This is William,' he told me. 'He's just back from two weeks' exclusion, and I'd like you to keep an eye on him. Last time he was in school he set his neighbour's head on fire'."
"I had a maths class who had seen me once before, last period on a Friday - on my first day's teaching. They were wild and I couldn't get them into any order. So next time they saw me they wouldn't sit down - they were screaming across the room, throwing pencils, rubbers, passing notes. Shouting at them was having no effect so I banged a three foot wooden ruler on an empty desk. "Unfortunately it broke into pieces, one of which whizzed past a boy's ear giving him quite a fright. A few minutes later the headteacher appeared - someone had phoned to say a class was running amok - and the boy told him I'd tried to kill him. 'Every teacher has his own methods of keeping control of a class,' he told the boy, and went away."
"I was in one school for just a day, so punishment exercises were no use and discipline difficult to achieve. A girl at the back of one class kept asking to go to the toilet because she'd burst her zip. Eventually she was so disruptive I sent her to the principal teacher. Five minutes later she was back, worse than ever. The rest of the class, seeing I was losing my grip, started acting up and by the end of the period it was complete chaos. On her way out the girl said: 'I'm going to bring my mum in tomorrow and she'll sort you out.' When the assistant head asked me to work there the following day I declined - she was a big girl and I definitely didn't want to meet her mum."