To toss my own experience in:

I my callow yoot grammar school, AKA, elementary school or grade school, was K-8. 9-12 was high school. After that, college. Grade school was sorta subdivided into K-6 wherein we had one teacher all day long for each level. 7-8 was called departmental (pronounced dee part men t'l, with equal stress on all syllables except the last).