This title and post made me laugh because I am in the exact situation. My son is 3.5 years old and daughter is 1.5 years old and they are by far, the ones that challenge me the most. I have done all the above recommended things such as separate his toys, give him special privileges or allow him to help with decision making etc...
The things that work best with my son are firstly to give him 1:1 time at break for 5-10 minutes, take him aside when things are not going well to give him a big hug and discuss things calmly (even when he is driving me crazy) and reporting back to his dad about his day, as we would do with the other kids and their parents. He is so proud to talk about the good things he did and embarrassed to share the not so good. His behavior during the day will influence the course of the evening, having a special treat or activity on really good days or losing privileges on bad days.