Oh boy do I feel your pain; I went through the same thing with my 2 year old. He was and remains my challenge. I tried everything punishment wise to get him to stop being so aggressive (like you, this only occurred during daycare hours). The only thing that has helped is to (1) nap him 1 hour later than the others (this way he has one on one with me) and (2) praise him for the positives and make sure he's my helper every chance I get. Also, the little things...let him sit in my lap during story time. Poor you!!