How to teach an 8yr old to ride a bike...

HELP!!! We need your assistance. I didn't push the issue of bike riding and just figured he would have learned to ride by now. I learned at 6 but back then my two sisters and I had one bike and there were no training wheels. I think having older siblings helped me learn early because I wanted to be able to keep up with them so I had some motivation to learn and in the 70's kids actually played outside so pretty much everyone knew how to ride. That's not my son's reality though. There are no older siblings and he doesn't have any neighborhood friends.

I first started trying when my son was 5 or 6 but I would be huffing and sweating to death trying to run next to the bike he always said he was afraid of falling. I tried again taking the training wheels off about a year later and still no luck so I backed off so I just let him ride with the training wheels on.

Now it's crunch time...the 3rd graders will be riding bikes in PE when they go back to school and he does NOT want to do it. He doesn't want his friends and classmates to know he can't ride. He has even asked me to let him skip school...

What do I do??!!!