My high school offered a class called Behind the Wheel, and almost everyone took it. It was classroom knowledge (no practicals), but it definitely gave us a lot of ground knowledge. After that, it was mostly our parents who taught us - most of our older siblings were too young to have younger kids in the car.

We did a bunch of stuff in the local high school parking lot, during times when it was empty. Stuff like learning to accurately judge where the corners of the car are, changing gears smoothly, backing up, etc. After that, it was time on small local roads, eventually graduating to bigger ones. Probably took about a year and a half, all totalled; had to fit things into everyone else's schedule and when we had a car free. My parents were kind of motivated, though - I was the last one and, once I had my license, they didn't need to drag any of our asses around anymore, lol.