Teachers can not just expect to put a wrench in society every time one of them decides that they are could be paid a little bit more. It would not be unfair to the government and the kids who have to lose out on their education because of it. Teachers should be fired if they strike.
Teachers strikes do change government policies. Even if they haven't changed them much at this point, they may be able to change them in the future. The government could make changes to a teachers pay or how many students are in the class based on a large amount of teachers going on strike.