I am interested in teaching TESOL in the USA, but what are the educational requirements to teach? I am leary about going back to school, to complete a MA in TESOL, but if that is the requirement, I can do so.
Can I teach TESOL to Adults with a Master's in Spanish? What about a Master's in English?

Murph

go to a college and get more information

The requirements depend on where you want to teach. Colleges and universities are going to require at least an MA TESOL, if not PhD. Community colleges require an MA.

For 'adult schools' and private schools, requirements vary. Some will hire you if you have teaching experience and a degree, regardless of what the degree is in. Others want better creds.

I'd identify what kind of situation you want to teach in, and then talk to some teachers to see what kinds of degrees they have.