I generally don't sweat it unless it's a weekday between 0700-1600. Most schools located on busy streets or state highways have yellow flashing lights on the school zone signs to indicate when to slow down. And if I see a school bus anywhere near the school, I slow down.
It's kind of a vague law, and it seems to have a broad interpretation. What if you're driving by an elementary school on a Saturday, and there's one kid walking on the sidewalk, and he's obviously high school age? What if he's 18? How are you supposed to know?