A thing that is close to most teachers and schools alike is your contract. Many of them aren't worth the paper they are written on, but most are. Schools will go to enormous lengths to get out of honoring a clause in a contract that is seen as detrimental to the school. Likewise teachers try to find loopholes that will help them break the contract so they can leave with a clear conscience, and feel they honored their part.
Let's face it, when a teacher realizes they made a mistake by taking the job, or have suddenly found another school that will pay them more money, they will try to get out of the contract. Many just up and leave with no word or thought for the mess they are leaving behind.
All contracts have a probationary period, usually three months. This time is not only for the school to see if your work is up to standard, but is also for you to see if the school is what they have presented themselves to be, is the school up to your standard? Let's be honest, if you can't suss out a school in three months you're a bit slow. At any time you feel that the school isn't for you within the probationary period you can leave without penalty or a feeling of guilt.
Be careful though. Your visa if it is a non-immigrant B visa is tied to the school. You quit, the school is obliged by law to notify the immigration division and cancel your visa. That gives you 7 days to get your house in order. Most of the time you will need to leave the country and re-enter on a new visa. This isn't the school being mean, it is the law. They can get into the smelly dark brown sticky stuff is they don't, just as much as you can.
Contract lengths vary with schools. Some go for a twelve month contract, others for two years, and others for ten months. Check the length of the contract before you sign it. Like most things in Thailand, contracts are negotiable. The obvious disadvantage for the teacher with a ten month contract is that it means the school doesn't have to pay holidays; which means you get stiffed for two months wages, just when you need them most. However, schools don't give uniform holiday entitlement. I know schools that give paid 6 weeks between academic years, plus 3 weeks in October, plus usually 1 week - 10 days over Christmas and New Year. Yet I know others that give three weeks out of the whole year, the rest you work or don't get paid. Whilst you are looking at holidays, don't forget the Thai teachers, they get an average of 1 week per year.
One thing I will say for Thai schools: They do tend to reward loyalty. The more you show the school that you want to be a part of the school, and stick with them for a few years, the more the school will support you in what you try to do and pay you better for doing it.
Contracts are there to be used by both parties, be ready with a bit of give and take, (you give the school takes) be honest with yourself, are you really worth the salary you expect? Should a non-teaching degree be worth the same to a school as a teaching degree? Yes, we know you could be earning twice as much in Korea or Japan, so why aren't you? Yes, we know you have commitments in your own country, so why are you here? Before you commit to a contract think hard and long about it. Don't rush into it, take a day or two, look at the options, then decide. Once you have decided though, stop thinking about whether you have made the right choice. Get on with the job, keep your head down and avoid the gossips. Honour your contract, and be honorable to yourself, your employer, and your pupils/students.
Should a school break your contract, you can always go to the Ministry of Labour, they will help you. You can sue the school for breach of contract.