I had a boy in my care that was very aggressive. He spent a lot of time in timeout! Multiple times a day. You sound like you are doing everything right but not getting the reinforcement at home. I put my trouble child in timeout in front of mom once. It was a shock to both of them. She then would threaten him that I would put him in timeout if he misbehaved at pickup. He was exhausting and they have since moved on to a daycare centre. My days are much better now.