I was finally going to give up and put the training wheels on Gareth's old red bike (that we got for his 5th birthday), knowing that it was probably a little small, but hoping spending some time on it would give him a little more confidence. We did that a couple weeks ago. There was some frustration still, caused by being a little too big for the bike and by the fact that you pedal backwards to brake. But it did seem to be working - he was zooming around on it and getting more comfortable with the slight downhill of the elementary school playground. Then he forgot to brake, ran into the fence, scraped up his elbow when he fell off, and I'm pretty sure you could hear the screams of anger at how his bike was trying to kill him all the way in downtown.
We took a few days off for him to get over his wounded elbow, but knew we needed to get him back out. He knew there was another bike in the garage that would fit him better, but without training wheels. We opted for that one last weekend, removed the pedals (but brought them with us, just in case). Still lots of frustration on his part about the weight of the bike and how it kept trying to tilt over or turn (always the bike's fault, never his). But he was seeming to keep his balance pretty well, even if he wasn't zooming along confidently. Eventually, he was ready to give the pedals a go.
Within a couple tries, he was riding with only a little help to stay balanced as he got started. He even was willing to try to start on his own, but kept getting nervous and would stop before he could get going. We went out again the next day and I brought my bike. I wasn't getting much riding time since he kept stopping every time he got to a curve and I kept having to help him start. Finally I told him that I was going to ride around the playground once, but that I'd be back to help him. Of course, while I was doing that, he got started all on his own! He's not to the point where he gets going on his first try 100% of the time, but pretty close. Still some confidence work to do, but we're hoping to get him out practicing regularly to buoy that up.