In my opinion it needn't be anything incredibly formal. It could be as simple as more experienced heroes partnering with those who wish to learn the ropes. Power control can be taught, if that's what's desired, along with more basic skills, like how to read a crime scene, disarm a mugger, or use a grappling device.

[She pauses, looking upward at nothing in particular. The music is bugging her, too.]

There are schools and gyms available for training, which is all fine and well, but there's also value in going out and working a patrol. It's something that simply cannot be taught in a classroom or gymnasium. I trained for this lifestyle since I was a girl, and even then I was nearly clueless when I first took to patrolling on my own.