How do you prepare soldiers for leadership schools?

I've always focused on empowering junior leader for leadership roles and entrusting them to make mistakes. The amount of learning that happens from understanding what went right, and what went wrong - WITHOUT GETTING CRUSHED is a vital lesson in developing our leaders and creating a real bench for our future military. We have to see the true value of a leader with muddy boots, boots on the ground and not just the well versed, school house Soldier.

there were some Correspondences courses that could help... or was...

Primarily by knowing the tasks they will be doing and the standards against which they are graded. You conduct training based on those tasks and standards. If I train someone poorly and they are not successful it's on me, I have ingrained in them a flawed method of doing things. However, I feel if they do exceedingly well, it's because THEY were receptive to the training that was provided to them.