Parents can be in the school but they have to sign in at the office w/ a photo ID. So parents do not walk their kids into the building in the morning (even kindergartners), they are dropped off at the door or in carpool, then the kids make their own way to their classrooms. If a kid shows up to class late, the teacher sends them to the office and they are marked tardy. Since my kids tend to get distracted, or it takes them forever to take their coats and backpacks off, they don't necessarily show up to class on time.
Parents can eat lunch with their kids (as long as they sign in) but no one is really allowed to volunteer for grades 2+, unless it's for a field trip or special event. For K-1 the teacher will put you on a volunteer schedule maybe twice per month if you want to come in. Otherwise there are no parents in the building.