B..
Turn those two around and you have my kids. We tried a lot, but in the end, it had to be his timing and his priorities. I was just savvy enough to capitalize on an opportunity.
We had gone to play in a gym with some kids. I knew by the way he was acting that he had to go. I told him if we went in his pull up, we would leave.
I took him to the potty and he went. We promised if he went everyday for a week, we would get him the color changing hot wheels. It worked. Never again had a problem.
I'm not above bribery! I think it's a combination of things. And the smarter they are, the tougher it can be! Keep big bro being a role model. Take opportunities to show him how it will benefit him. Bribe! Keep little toys around to reinforce good behavior.
Hang in there. He won't go to K without learning!