I just came back from Imigration yesterday where one of the teachers in our school had a problem with his VISA (ran out of a non b and had not stamped the 90 day registration)...
They are usually very nice down there, and this was just like all the other times there...
They did tell me that some of the foreigners here in town are not always very good at stamping in every 90 days... Please do that.
It is not schools duty to make sure the visa is in order, that is the holder of the visa...
Any school will not be responsible if YOUR visa is not in order, YOU ARE... so please check your visa's and the 90 day stamp...