Hi there lydialeyba... Welcome to the café! B)
Well, to over-simplify and answer your question directly, the penalty for over-staying your visa if you were to get caught is deportation. Pretty much the same as in any other first-world (or sixth!

) country.
However, and I don't know your nationality, Spain is famous for being pretty lax with immigration. Not at all, say, as stringent as the US is. Personally, I don't know of a case of an English teacher being deported personally. That doesn't mean to say that it couldn't happen though.
I'd be interested to hear if anyone else has heard of this happening. Feel free to post that information here. Or, and I'd do it myself by I feel lazy this morning

, you could
search the board for such examples. We may have some info lying around in the corner somewhere. (
Comisario: You can refrain from posting as yourself or as one of your multi-cultural alter-egos as we're sure you'd be happy to tell us about one of your conquests. We'll pass though... :angry: )
Everyone else though...
POST AWAY!!