When should kids start tutoring?

When there is a reason, rather than on a schedule. A child who is coping, enjoys the subject and finishes their homework does not need tutoring because their classmates have it. The point to start is when something specific has gone wrong — a topic that never landed, a board change after moving country, a slide in confidence — or when a child is far ahead, bored, and the school cannot stretch them. Both are good reasons. Drifting into it because everyone else has is not.