My kid is a HIGH OBP and take a lot of pitches batter. He won't swing at a pitch one inch out of the strike zone and often will take a strike (or two) waiting for the pitch he wants to hammer. As a dad spectator, it's frustrating because hits make noise and get attention.
Meanwhile I know other kids who go up there aggressive and rip at the first close pitch because they're thinking 100% hitter and zero percent patience. And, those are the guys getting 2 or 3 hits a game and getting attention.
While my son won't budge, if your son is considering being more aggressive, you might want to endorse it.