I did the skippy 3-day school and that is how I heard about karting. Basically, everyone who showed up with karting experience kicked butt on everyone else.
There were more students than cars, so we went out in shifts. During one interval of downtime I was standing next to one instructor when the fastest drivers in the other group went by, all packed together and racing. The instructor radios another instructor and says “I see the karters have all found each other as usual.”
I asked a few question and was told (1) seat time, i.e., practice, is just as critical in auto racing as in any other sport, you don’t expect to pick up a basketball for the first time and go straight to the NBA and you shouldn’t expect to get in a race car and be ready to driver it correctly, (2) the best way to get seat time is karting, and (3) by the time you progress up to a shifter kart, the next performance step is an Indy car, i.e., a shifter is harrier than an Indy Light.
On top of it all, karting is WAY cheaper than the alternatives. No wonder the F1, Indy and even NASCAR drivers drive them in the off season. It’a really a no-brainer to start with karting.