How are you "training" them? It's important to drill down into what they're struggling with before you throw resources at them.
I've found that code reviews are the best way to mentor and transfer knowledge. And it goes both ways: you review their code, they review your code. When I'm explicitly training someone, I get them to review my code and I occasionally throw in some minor curveballs that I expect them to pick up on in the first few rounds (e.g. obviously incorrect conditionals, some convoluted loop, leaky interfaces, etc.) If they stamp the PR without picking up on those items, I highlight it using a "do you think this is correct/is there a better way for us to do this" line of questioning. 5-10 or so PRs later, they become the first to spot those issues :-)
I've found that code reviews are the best way to mentor and transfer knowledge. And it goes both ways: you review their code, they review your code. When I'm explicitly training someone, I get them to review my code and I occasionally throw in some minor curveballs that I expect them to pick up on in the first few rounds (e.g. obviously incorrect conditionals, some convoluted loop, leaky interfaces, etc.) If they stamp the PR without picking up on those items, I highlight it using a "do you think this is correct/is there a better way for us to do this" line of questioning. 5-10 or so PRs later, they become the first to spot those issues :-)