C.C.
My son attends Pre-K through the school district and his first teacher used 1-2-3 Magic and it worked well. We use our own version of 1-2-3 at home and only for little things. Big things; like running away from us isn't counted because it's an absolute no-no and dangerous so that's an immediate time out...the same for hitting and other extreme behaviors. As long as you both are consistent with him it will work. It's the healthiest way to go because they are given a chance to decide whether or not to continue the behavior and deal with the consequence. It's not going to be easy to implement for a 3 year old if you haven't already been doing it but after some time it will work so don't give up when he gets worse in the beginning. Best wishes.