As an outside observer, I would say you were/are over-reacting to the note from the teacher. I agree with whomever suggested that you either follow up with a meeting or at least a phone call with the teacher to address his concerns. Then you both get immediate feedback on each others suggestions and can agree on the solution.
Actually, reading the email I think he is trying to be helpful, in making suggestions that he feels might make it easier for your son. For example if he is carrying the snacks in his backpack vs. in his locker, then he can just step out into the hall to check his BG, eat one quickly vs. going all the way back to his locker. IMO, I think it is fair to have him step out to the hall to eat vs. eating in class.
It sounds like his teacher wants him to succeed, and he is only pointing out that the D is affecting more than just the snacking in class. As for him not asking questions when you gave your presentation - he may have thought it would be no big deal, but now that class is in session, seeing that it is and what you set up to manage it is not working as well as maybe it could be. Try to take the suggestions as just more information on how to better manage his D not that your kid is a bad kid.
One rule of thumb I read regarding Lantus doses was that your BG shouldn't change more than 40 pts up or down overnight. If it does this 3 or more days in a row then it is time to call your endo to discuss dose changes and go back to some middle of the night checks. So I am glad you endo was lowering it - I hope this helps.
I am sure it is REALLY hard for Drew right now. If he was stressed about school and being picked on for other reasons, then D could just be putting him over the edge. It has not been that long since he was diagnosed, so he is probably still coming to terms with it. That said, I agree you need to make sure that he is also being responsible for his care - like checking his BG after treating for lows (sounds like you are on that one!) and checking a lot more. Could you make a rule for him that he has to check before each class or every other class and then check his meter when he gets home?
Please don't take this post to be critical of you or judging you. I do not mean it that way. I just know that for me, I often appreciate an outsiders perspective before I can think about something rationally that I have reacted to strongly emotionally. So I hope this helps and doesn't hurt!