You gotta educate 30+ children (some with special needs who likely aren't getting the assistance they are legally entitled to), the school administration, testing & overview policies (which treat teachers as totally incompetent here in the US) and deal with the kids parents to top it off.

Each of those factors alone can make for a bad work environment, combined it is a living nightmare. Plus the pay is very low, so its not as though you are able to afford much.