Hi champagnesupernova:
I had my rant on the other feed so would briefly only suggest this: you probably know a few things that concern you or you're not clear about. My advice is to make a little tick list (just a one word thing to remind you to ask).
It could be as silly as plimsolls - your DS has changed shoe size - should you just send these in with him or do you come in when you collect him/ drop him off and swap the shoes over?
Anyway - you'll already know what you do and don't understand about his class or what's bothering you (maybe no books home yet) - so make a little list and then select 3 key questions that you really want to have answers to. This way you aren't monopolizing the teacher's time (she/ he will have a lot of other parents/ carers to see) but you are not just sitting there.
If this is year R - the obvious question is 'Are you happy with how XXXX is settling into your class?' - it's neutral but it is giving the teacher permission to say if there are a few 'issues'.
Finally I would say that if you convey to the teacher(s) that you're concerned to honestly understand how your DC is doing and interested in their opinion, they will open up. But it's about building relationships and letting them understand that you will greet good and bad news with equanimity.
Welcome to the club!
HTH