Imagine waking up every morning not knowing if you have any work and if you do have work, where you will be going. Your whole day will be dictated by one phone call. This phone call will determine whether you earn any money that day and could send you anywhere within a 40-mile radius of your home.
Do you remember your first day at a new school, feeling nervous about meeting the staff, the pupils and how you will manage to navigate your way around unfamiliar surroundings? Now imagine having to do this every day for an entire week, a term or even a year.
You must be adept at following directions, often received over the phone while you are still half asleep. You must make sure you carry a bag fully equipped with stationery at all times. You must dress smartly and smile sweetly. And you should slide seamlessly into each school's curiously idiosyncratic education system chameleon-like.
This is your mission, should you choose to accept it. This is supply teaching.
You set off, and after having driven through four counties and as many different weather zones, you arrive at your destination; possibly shaken and certainly stirred. Your suit is slightly rumpled, your skin carries the light sheen of perspiration and your smile belies the faint hysteria that arises from a journey that has been fraught with road works, missed junctions and adrenalin-fuelled anticipation of the day ahead.
At reception you are greeted with: "Ah, so you're here ..." and the words "at last" hang in the air, as you are handed a badge with "Supply Teacher" emblazoned on it in bright red letters. It might as well read "Kick me now", you muse while pinning it to your lapel with a shaking hand.
When you reach the appointed classroom, usually on the top floor of the furthest building, the door is locked. A line of pupils looks at you expectantly for a few seconds. Then, when they realise you don't have a key, they go back to prodding and poking their mobile phones - or each other.
Ten minutes later, a caretaker finally lets you into the room. The usual battle of wills ensues as you ask pupils to sit down and remove their coats. You wish they would remove their sulky expressions too.
If you're lucky, work has been set. But it may be a subject alien to your specialist knowledge. You persevere amid various observations along the lines that you aren't a "real teacher".
Sometimes the work runs out half way through the lesson and you are obliged to improvise. Where is that unicycle and set of juggling balls when you need them?
Break and lunchtime may not provide the welcome solace you might think. One staff room is like the Marie Celeste: the door swings softly to and fro as yellowing letters flutter unread on the notice board and mouldering coffee cups prove that this place was once - a long time ago - inhabited.
In another, you unscrew your flask gingerly, not daring to risk the minefield that is "Using Somebody Else's Mug" and sit down quietly. If it's a good day, someone will say "Hello" to you; if not, you will sit there invisible, willing the bell to ring.
As the day goes on, you may experience an extremely challenging class and have to call for assistance. A member of senior management will briefly descend from a cloud and walk around the class, which has miraculously fallen silent, before smiling beatifically at you and gliding out of the door again. The silence will last precisely the length of time it takes the SM to be out of earshot.
Or a passing teacher, in an attempt to be helpful, may come along and tell the pupils not to take advantage and misbehave just because they have a "supply teacher". In America, you would be called a "substitute teacher" or a "sub". Here, you realise, you are regarded by some as a sub-species of teacher; sub-standard, sub-normal, subhuman?
You simply smile sweetly. You are a professional. You will try to do your job to the best of your ability. "You are beautiful, no matter what they say." And you need to make a living.
At home in bed, you toss and turn wondering if you will make enough money to cover the bills. You have a restless night's sleep wondering if the phone will ring in the morning. You are only ever two or three phone calls away from pecuniary collapse.
This is your life. Yesterday, today and tomorrow. You are a supply teacher.
Jo West, Supply teacher, Cardiff.