Brendan Acting Up, but Adam is Sleeping Better!

Brendan has been acting up at daycare lately. He's been "written up" by his teacher every day this week so far for various things...
-play-biting his friend while playing Power Rangers (he said he was being the dog Power Ranger- whatever that is?!)
-dumping sand on another kid's head on the playground
-talking back and saying no to his teachers
-not listening during their lessons
-copying his friends (don't all kids do this sometimes?)
-yelling at his teacher when he got in trouble
and the day he didn't do anything "wrong", she wrote him up for kissing his friends too much(?!)

None of the incidents were too serious, but I certainly want to nip it in the bud. I don't understand WHY he's acting up...can't think of anything that's changed at home that would make him act differently. They recently changed teachers in his room at daycare, so maybe he's just testing her? I don't know. She seems to write him up for every little thing. (including for kissing his friends?!) Joe's starting to think the teacher just doesn't like Brendan. I wonder if he's been doing things like this all along and the other teacher just didn't think it was bad enough to write up?
Seeing as it is after-the-fact by the time I pick him up and get home, some things, like time out, for example, for something that happened hours ago doesn't seem appropriate. I always have a talk with him and we talk about why he shouldn't do what he did, and tell him what he needs to do from now on (be nice to his friends and teachers, listen when they sit down for lessons, etc). And he doesn't get any treats or anything like that that night. And then when I drop him off in the morning I remind him to be nice to his friends and teachers and I ask him what he needs to do at lesson time and he says "be quiet and listen, and do what my teacher says". This has worked in the past when he acts up for 1 day, and then he's fine for a long time, but this week it's been something every day!
I'm not sure where to go from here. I guess the next step is to take away toys/priviledges at home.

On a good note, Adam is sleeping SOOO much better! In desperation I moved his crib into the bathroom off our bedroom (it's a big, long bathroom with plenty of room for the crib) because it's still close, but has a DOOR. So now we're in the process of training him to fall asleep on his own (which we SHOULD have been doing since he was born, but we didn't have him in a room that the door could be closed, so we were feeding him a bottle until he fell asleep and then putting him in his crib...sometimes at 9pm he was still awake!). Now, we give him his "night night" bottle, and if he doesn't fall asleep, well, it's still bedtime anyway. I take him into the bathroom, turn on the nightlight and some soothing music and put him in his crib, close the door and walk away. He, of course, cries, but it is only for a few minutes now before he falls asleep. OMG I can't tell you how wonderful this has been!!! Why didn't we do this sooner?! I actually have part of my evening back and don't have to stress over trying to put him to sleep. Now I can focus on Brendan and getting things ready for the next day instead of falling into bed myself as soon as Adam goes to sleep. Now he is in bed by about 7:45pm every night. I can't wait until we can put the addition on our house, which includes a bedroom for Adam, but in the meantime the bathroom will do!