Do you have a documented disability already? I would definitely have all your ducks in a row with regard to documentation of disability, and the accommodations that your private psych thinks will be most appropriate (rank them in order of importance/impact, too), prior to speaking to the school officially.
I would also second giving the teacher a week to make her own assessment of the class. In addition to not skewing her perceptions, it also gives the teacher a chance to take a breath first, which is always helpful in eliciting cooperation/collaboration.
But overall, I would ask, on behalf of all of my colleagues of goodwill and (dare I say) competence (I can't speak for the other ones), please do not withhold vital and relevant information about your child for unreasonable periods of time. From my experience, when the system finally gets the report, six months or a year down the road, often accompanied by demands that the child's academic or behavioral struggles be fixed immediately, the fact that this information was known to the parents but not shared with the school is most definitely not conducive to a collaborative relationship.
You don't have to speak to the classroom teacher about a disability first. If you are winding your way through the 504 process, the person to speak with would be the 504 administrator, anyway. Teachers don't necessarily need to know specific disabilities. They just need to know the accommodations that the 504 team decides on.
