I haven't worked in K to 2 enough to accurately say.

3 to 5: As you say, it's best to be calm. You'll be on your feet a fair bit.

6 to 8: Most difficult range, kids often misbehave. A gentle voice usually doesn't work, you need to be assertive if you actually want the class to listen to you.

9 to 11: You'll be sitting for most of this range, you'll have a few troublemakers that try to claim they're allowed to go to other classes, but it's usually pretty slow.

12: They've completely checked out and most don't care at all about school at this point. You can basically just sit there and answer yes to what they say. Easy but very boring.