I've taught over 300 adults and kids (mostly adults) how to ride. Most adults require two lessons of two hours each to get all the way to confident turning (figure-8s) and shifting gears; a few do it all in one lesson. My method is described here:
Learn To Bicycle At Any Age
Several other instructors and groups around the U.S. have developed this coaching as a specialty. Susan McLucas and Pata Suyemoto of the
Bicycle Riding School in Somerville, MA offer group classes and have taught over 2,000 adults. Bike New York offers
adult learn-to-ride classes in the New York City area. In Canada,
Can-Bike's Adult Learn To Ride 1 class is offered in various cities.
John Ciccarelli
Bicycle Solutions
"Expert Coaching for Confident Cycling"
San Francisco
League Cycling Instructor #453