Maybe if your son hears about the Bring Your Bike to School Day from someone other than his parents, he'll get more interested. Our son balks at all kinds of things that we as parents suggest, but he'll listen to teachers.
That said, our son is 7 and will still not ride his bike. He did not use his scooter or his tricycle either. He is just very cautious. He has told us that he would try to ride the bike again if we put training wheels on the front wheels too.... We're going to try to get him going this summer. He'll be at my mom's for daycare, and her neighbor's kids are 2.5 and 4 and are always racing by on their little bikes. Maybe that will encourage our son.
You will probably find some other threads about bikes if you search. I remember one bit of advice I thought was good was having the kid ride the bike in the grass, so that any falls wouldn't hurt.
Good luck!
