Even if you're not sure, I think you have to SEEM sure. Fake it if you have to, but don't let them see you doubt.
I don't know, this may not be a hard and fast rule. I opened a dialogue with our principal early in the school year about DS (while he was still in K) and talked to her about my concerns for him if he is not kept challenged. We talked about the pros and cons of grade skips, differentiation etc. I wanted her to know that I had really considered these things. I even voiced reservations about grade skipping. I didn't share his scores with her at that time.
A few months later, I talked to her again to let her know that trying to do differentiation wasn't working very well because it was too much of a demand on the teacher. I told her I was leaning toward requesting a grade skip for him. She gave me her objections, but I came back the next week with some information and his scores to back me up.
I think using this approach sort of let her get used to the idea of grade skipping him. Of course, I know her since my DD has been at that school for three years already. I know that if I just show up and demand something she really digs in her heels.
I don't know if any of my experience can help you...so much depends on the personalities of the people involved.
