My certification process had the possibility that you might fail your actual skill level test, or be able to pass a higher one, meaning those cards might not go 1:1 with actual skill. Also, a pay level system where Skill-2 is full pay, Skill-0/1 is much less and Skill-3+ is greater pay.
The skill is pretty basic, which is likely why there's no need to recertify for cars today.
The vast bulk of driver training is rules, rather than physical skill. There is absolutely skill involved, as demonstrated when my mother tried to teach my brother and he lithobraked the car using a fence. But it only take a little practice to become adept.
I, personally, am self taught. We used to have a back lot, and my mom would let me drive the car around it. It has a manual transmission, and was great at throwing rooster tails of dirt up in the air. It was great fun. Learned all about friction zone, shift time, fishtailing the car.
I am self taught on a bicycle, self taught on a motorcycle. The trick on a bicycle is going fast enough the first time, then its easy. During my adventure, I couldn't figure out how to stop (I dragged my feet, wished I was learning on a girls bike >.< ). By about my 4th try, I had the coaster brake down, and was skidding in the dirt. Whee!
My first motorcycle was a moped, I road it around the block the first day I got it. I, literally, put 50 miles on it that day. Moved up to a scooter, had mishaps, survived. When I got my "real" motorcycle, I learned to shift in a parking lot (friend rode it off the lot for me). 1/2 hr later I was on the street. I started riding in 1983-84. I finally took a formal class (MSF course) in 1989.
It has not been a scratch free learning experience, looking back, nothing I learned in my classes, likely would have prevented the mishaps that I did have. I do recommend them though.