  this morning at the park one of our neighbors was there with his son, who was on his big boy bike with no training wheels for the first time. It was so exciting to see them, we pulled out Aidan's tricycle (he'll be getting a real bike w/training wheels for Christmas) so Aidan could be like the big boy.
The dad was explaining that they'd tried to remove the training wheels a few times before with no luck, much falls, never really balancing. Then, the uncle got the boy a scooter (the two-wheel zappy, no motor, small skate wheels) and the bike was kind of forgotten for a while.
The boy played so well with the scooter, and it turned out to be the perfect middle ground of control and balance, by the next time they tried the bike with no training wheels, his balance was adequately mastered and today he was riding very well, practicing braking and getting back on (after many falls, which dad took like a pro with atta' boys and up you goes). He also said, and I've read this elsewhere, that the bike with training wheels was much more stable than a tricycle, and more realistic to maneuver like a real bike. 
