Just one question, asked again and again… “Why?”
“When you did that lesson, why did you do it that way?”, “Why did you talk to him rather than her?”, “Why did you sit there?”, “Why did you change your plans?”, “Why didn’t you change your plans?”, “Why do you think you’re feeling low?”, etc.
Everything a trainee does, regardless of whether it went well or poorly, can be brought back to the question, “Why?”
In fact it’s especially important to ask when things go well. You’d be surprised the amount of un-Christian, un-reasoned “that’s just the way we always did it” that goes on!
How do you know if they’re doing it with gospel motivations and values? You need to ask them “Why?”