One big thing about America is that most "qualified" or "certified" professions do their qualification at the state level. You would have to contact the state education board of whatever state you were interested in to find out their requirements - which are often quite US-dependent. (I.e. a certain number of hours of training in specific subjects at the university level.)

I'm not sure if a foreign teacher qualification is transferable to most US states. That does leave private schools, however.

Actually, there is. And I recently read an article (in the NY Times, I think it was) about the Army recruiting from overseas for precisely that program. There was also, however, a recent article about how long it is taking for the US to process citizenship papers for those who have earned their citizenship through military service.
Cheers,
Bev