Tina's in 8th grade, Gene is in 6th, and Louise is in 4th. They all go to the same school, Wagstaff, which is in walking distance.
It's got lockers, but it's also got Elementary School style setup, because there doesn't seem to be a situation where the kids go to different teachers for different subjects. Also, they're together quite a lot, given the difference in grades. There doesn't seem to be that many kids at the school, despite the fact that it's a public school in a Coastal town that can support an amusement park, a minor league baseball team, and gimmick boutique shops (if only temporarily).
Andy & Olly are in Louise's class, Jimmy Jr and Zeke are in Tina's class. I'm not sure where anyone else fits in. I don't think Gene has ever attended class, but he does do extra-curriculars.
Are there facts I'm missing? Let's solve this thing!