Jonathan is done with training wheels! He has been asking me to teach him, so on Sunday we took off the training wheels and had a go. He figured it out after about three tries and without any major falls. He is pretty coordinated and had been riding for a while, so I think that helped.
The first 2-3 times I held on to his front handle bars while running next to him. After doing that we tried again, but this time I let go of his bike for a second or two and then grabbed back on. When I did that (without telling him) he initially was scared a little bit, but then he quickly realized that he had been riding by himself for a second or two. That was enough of a confidence boost for him. I did that again, but then he told me that I was "distracting him" and that he really just wanted me to give him a push. OK then...he got a push...and off he rode!
Here is a video a few minutes later showing off his new skillz to Mom and sister.