Let's face it, good programmers are usually not good teachers or mentors. And good teachers don't know about the specific stuff on your project.

We do pair programming for many years, it works pretty well in terms of training. The best part is you don't have to pull your hair off to come up with a perfect training plan (which most of the time does not very work as expected). You can consider skill is somewhat infectious, and then by pairing and switching pairs, the skill will naturally spread across the team in a passive manner.

If your project cannot afford pair programming, maybe you can exchange the training budget with just pairing with graduates or make it only happens in the onboarding period.