There seems to be a trend in some American forums for the use of 'alot' instead of 'a lot', e.g. 'I had alot of those when I was a kid.'.
As for teachers, I really feel we credit them, as a species, with far too much. Whilst there are some great ones out there, even they would own that they are certainly not the founts of all knowledge many people believe them to be. Whilst I would expect an English teacher to have personal high standard of English, I probably wouldn't expect that from, say, a Maths or History teacher. Saying that, my son once had a Maths teacher whose spoken English was so poor none of the class could understand what he was trying to teach.