If you want your reports to learn on the job:
1. Make it part of their annual goals (e.g. attend a conference, get a certification, compete in a competition).
2. Throw them in the deep end, a little beyond their edge, and be okay if they fumble around a bit.
3. Make them teach. Give them stuff to understand and present to your team or other teams. That forcing function will give them a mechanism to immediately exercise their newfound knowledge/skill.
4. Make room in your project schedules for it. They'll learn on their own if they have the time, or they'll invent something. The ones that don't are your bottom tier.
My first boss sent me to Siggraph my first year to drink from the fire hose. He also asked me, on my first day, what I was worst at of all the areas of programming I was aware of (Windows UI) and assigned me three months of work writing custom controls... I did it in six months, and I've never been able to thank him enough for teaching me, right off the bat, that your people are your greatest investment, that optimizing for the project is rarely the right choice.