Brookline MA has k through 8 in the same schools….no separate middle schools.
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Actually, the school I taught at is K-8. About 20 years ago they built a separate building for 6-8, but the kids all still mingle. The ‘middle schoolers’ still play on the swings and run around on the playground during recess. I think it’s so much better for them than just walking around acting cool during their breaks.