Edit to respond to cross post: To involve the principal, you go to the teacher with ideas and brainstorm. Teacher reaches a limit, either doesn't want to help, wants to help but doesn't feel capable, or doesn't feel she has the authority. Then you suggest the principal might help you all out and wala, the principal is there and you are all on the same side.
Yes, this is the approach I used to involve the academic director after conferences. ("Oh, you don't have the next level of assessments? Hmm, do you suppose the academic director would? Oh you think I should ask her? Lovely then!")
Since the AD is an admin and is the one who's supposed to handle GT issues, do you think I'd have to get her OK to involve the principal? I'm pretty frustrated with her responses so far. Also it's been 5 weeks of trying to get her to tell us for sure whether someone at the school can give DD the one subtest she's missing to get 2 more possibly qualifying clusters for DYS. She ignored my 3rd email, which was sent last week letting her know we went ahead to submit the app without that last score but it could still be really helpful to have.
