1. You're not the _English_ teacher...
I had, not unreasonably, kind of assumed I'd be assisting the teachers in the ESL classes - you know, teaching English. What I did NOT realise is that these are bilingual schools, where classes are actually taught in English, and THAT's what you're expected to help with! I never studied science past Year 10, so to find myself teaching Year 9 biology has been a bit confronting, to say the least. History and Geography classes have been easier, since the teacher wants me to talk about the same time periods and phenomena as they occurred in and influenced Australia. Anyway, be warned - you won't be explaining past participles in English class, you'll be explaining the pronunciation of 'glomerulus' to your science class. Yes, I had to look that one up too.
2. The Spanish and organisation do not mix
There will be times when class will be cancelled, and the only way you will find out is by attending an empty classroom. There will be times where the class will have an exam during your timeslot, and the only way you will find out is by walking into the middle of an exam. There will be times where you walk into the classroom, the teacher pushes the textbook into your hands open to a particular page, and walks up the back of the room to wait for you to begin class. Basically, there's no loop to be in here. People will forget to tell you things, not think to tell you things, not really plan ahead where you're involved, and generally leave you wanting to strangle someone or something until you get used to essentially getting screwed over a lot. Ask for a list of public holidays and school-free days, find out where the teacher's noticeboard is and learn to check it so you know who's on camp and when, and be prepared to smile and say, "Not a problem," when someone apologises for the general Spanish apathy making you look the fool yet again. After four or five months you learn to just go with the flow and not get mad when things don't work right - the entire Spanish nation apparently runs on this principle, from what I've seen.
3. WorkChoices does not exist in Spain
Yes, we have a contract. No, that contract is not much use. Nothing is really spelled out clearly, so exactly what our job entails is up for debate. Supposedly we work 12 hours a week, and schools can allocate that time as they please, whether it be for classes, English tutoring sessions or meeting with teachers. Theoretically our job also includes class prep. Whether those 12 hours and that class prep intersect is one of the great unknowns. In my case, I was given 12 hours of class, so anything else comes out of my own time. Teachers also don't co-ordinate my classes with each other, so there have been weeks with no prep work whatsoever and then weeks with hours of reading and research to do. Oh, and then there's my favourite - if you miss a single class through illness or other reasons, you're obliged to make it up, but the school can cancel any number of your classes with no warning and no such concessions are made to you! Basically, be prepared to possibly be screwed over, and if you stand up for yourself, be prepared to potentially have your own contract used against you.
4. Not all teachers are created equal...
It's been one of the bigger revelations of the year for me, but there's a wide variety of teachers and teaching styles, and some are light years ahead of the rest. The good teachers are a joy to work with, but be prepared for the less delightful teachers as well. Some of the bilingual teachers 'don't speak' English, some can't or don't control their classes, leaving you standing awkwardly at the front of chaos, some teachers seem to think YOU're the teacher and THEY're the assistant and suddenly have no clue what they're doing once you're in the room. There's really not a lot you can do - you can't really reform bad teachers, though you can try and insist on a modicum of preparation and advance warning from the teachers. Otherwise, just don't be surprised when you suddenly find yourself in front of 30 noisy, rowdy teenagers with no teacher in sight.
So those are more or less the biggest surprises I had once I started classes! Did anyone have their own "Oh..." moments once they started at their school? First-years, any things you've been wondering about your transition from student to teacher?