Thanks for the comments. The ride without a seat is a good idea. Definitely need to get him to slide off the saddle when coming to a stop as well. His saddle is about 4cm too low right now to accommodate this habit. I think I had the same habit as a kid.
I also realized that he doesn't do well with Daddy being a teacher sometimes (even though I'm a teacher by profession). I bet if I get one of my cycling buddies to be the "expert", he will do whatever they say. That's how we got him to dive into a swimming pool without the floaties!
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It's like riding a bicycle