You are getting great advice here. Don't feel badly about mistakes you may have made -- this is such a huge learning curve for most of us! (And weighted against us as parents, truly.)
Do you happen to have a trusted friend or relative who is a solid editor who could review written correspondence to the school before you send it? I ask because my DH and I perform this task for one another (when I was younger, my mom would do this for important applications, etc.). If we are sending something to a teacher or the principal, whoever wrote it well almost always have the other read and edit it first. I have found that it is so helpful to have another set of eyes, rather than just my own point of view, looking over these kinds of messages.
Another piece of advice I learned at a work training event is to try using "What, where, how, who, when" phrasing, rather than yes/no questions. Then be quiet and take notes. Example "How might you be able to address DS' learning needs?" "Who has experience with children like my DS?" "What are the schools concerns about this situation?" It gets a lot of information on what the other party is thinking without letting them slip into easy answers so quickly.
Oh! I just remembered something a friend told me before I had my first child. She said that one of the hardest things to learn as a parent is that you must be their advocate (I think she was saying with doctors), because there is no one else to speak for them when they are young.
