There wasn't such a thing, when I started riding in 1971.....  the learning curve was steep; and the price paid to learn was generally some skin. 

Trying to keep costs in line meant learning to wrench on your ride, as well.

It took a lot of 'pluck' and knowing someone who knew more than you did, to bail you out when you were learning..... most of the time, that meant talking over the magazine articles with your friends and trying to de-code what your engine's sounds were trying to tell you.

Safety gear was pretty much whatever you wanted it to be.... FF helmets were just starting to come into use, body armor didn't exist except for football players.... motocross was just starting to get specialized gear...

Over the ankle lace up boots, and a denim jacket were pretty much the only alternate to engineer boots and a biker jacket.

So, My formal training went something like "there's the gas, there's the rear brake.... here's the clutch."  "Don't fall down".

"This is a jump.... land on the back wheel so you don't crush the front rim".

There's lots of wisdom gained from learning to ride without any training, and a sense of self-confidence.  Wrong things are sometimes learned, but a rider who is really into the sport and keeps informed about riding, the bad habits can be un learned.

I really appreciate my BRC class from Team Oregon.  I was clueless.  That class saved me from myself.

The magic and mystery of learning to ride without training, that's worth something and it should not be put-down as unworthy learning.  There's also magic and mystery to learning to ride "with" formal training.

I started late in life so I took the BRC. As a matter of fact, I'm not sure I would have ever ridden if there wasn't some kind of formal training.

Dave,

    My personal belief is that formal training will increase the speed with which the basic skills needed, will be acquired. It doesn't have to be MSF..... a structured presentation with reviews, demonstrations, drills and evaluation can be one on one, or class room based, hands on... whatever. As many people as there are, with as many different ways that they learn, one program does not fit all.

   I can't figure out any way to evaluate how many go the route of formal v. taught by peers/family....it's not like there's a stamp on your liscense that says it.

   Then you get to the point where you have to question which is really the case; as soon as you define it one way or the other, the bragging rights are established, and people start altering their answers to meet their perception of 'cool'.  (I saw a lot of this when I was on recruiting duty with the USN.... we'd occasionally take the applicants to see a Navy ship and give them a tour of it...... I'd ask the sailors 'how many of you walked into the recruiting office on your own, without any contact with a recruiter?'  every time I asked, nearly 100% of the sailors would hold up their hands. :)  Yeah, right!