I can't get my child to tell me about trouble with friends.

Recalling events and recounting them in order is a heavy demand, and it often ends in "I don't know." Avoid the tired time right after coming home; after a drink or rest, ask with concrete two-choices such as "outside? the classroom?" or "with ○○?" Looking at pictures, photos, or the day's schedule makes recall easier. Rather than pressing, an adult offering a guess ("did something like this happen?") for the child to answer yes/no also works. When confirming facts is hard, use adult routes too—the home-school notebook, the teacher's information—and, above all, gently accept the child's "I felt bad" feeling.