I can only speak to the public elementary and middle schools but here's my experience in both in school and during contract teacher evaluations (that SMOE performs to hire). My first set of CTs was a mixed bag. One teacher slightly younger than me, very fluent including understanding most idioms (she studies them), another one brand new teacher, pretty fluent in standard English, and the other was not fluent but if you spoke really slow you could sort of conduct a complete conversation. The following term (last term) I got a teacher (who on paper looks really good) who is pretty fluent conversationally but in the classroom her grammar would sink (don't know why) and make me cringe and I'd have to covertly correct her to the students. This term, I only have one and it's the only one I've had since I've been here (the really fluent one) but I only teach one grade with her (I wish it was more). I am now (more or less) teaching the other grades alone with help from the homeroom teachers when they can. During camp I teach with the contract teacher and (I also evaluated incoming contract English teachers) it's my experience that the ones who pass are generally really fluent. The one at my school now is exceptionally fluent. I don't know her idiom ability, but she understands just about everything I say and I have no trouble understanding her. It was almost the same with our previous contract teacher. The English ability in my school for the most part seems to be by age level, from the oldest having virtually no English to the youngest (with a few exceptions) having excellent fluency.