See, I think it was a huge mistake to put 9th graders in high school, an opinion that was greatly reinforced when I started working for a school system. Becoming old enough to drive, which happens during 10th grade for nearly all students, makes the most natural dividing point between growth stages.
Of course these days with graduated licensing, higher insurance premiums, and states simply raising the driving age keeping teens off the road for longer that’s becoming a much less relevant dividing point.
Middle schoolers are a completely different species and must be separated from the rest of the animals both for safety and scientific research.
Married to a middle school teacher, and subbed for many years, mostly in middle school.
That’s the way the schools in Rockville Centre, NY did it when I was in school.
Now they do the 6-8/9-12 split. It was mostly due to reduction in school aged population. The high school building handled 1000 students. For years that equated to three grades worth of kids in the district. Then the grade sizes shrank. Since there was a movement to switch to the Middle/High system they seized the opportunity. I dare say most school districts on Long Island used either the 7-9/10-12 or 7-8/9-12 model back then (70’s). I had friends in neighboring districts; they too used 7-9/10-12. And 10-12 was actually called Senior High School. I believe my high school diploma listed it as such, and it was on the school façade until the switch.
Elementary schools were all KG-6.
Where I grew up, grades 7-9 were called “junior high school” and taught in their own building. I’ve since learned my junior high has since been redesignated a “middle school.” This sort of redesignation was common nationwide at some point, I heard.
I’m going to confuse things by saying that I went to a “senior public” school. 
In Whitby, Ontario, in the mid-1970s, there were three levels of schools in the public system. First, there was K to grade 6. These grades were in smaller neighbourhood-scale schools, often within walking distance for most students.
Grades seven and eight, and only seven and eight, were at Whitby Senior Public School, and students from all over town and beyond were sent there. The school was also laid out in an open plan with ‘pods’ containing more than one classroom. For some reason–the layout, the relative isolation, the removal from familiar environments, the influx of strangers, I don’t know–this seemed to encourage a Lord of the Flies type scenario among the students. No-one I know liked it there.
I now have the impression the place was somewhat experimental, because now it’s a K-8 public school. Of course, also, now, Whitby has a much larger population.
Grades 9 to 13 were in high schools, of which there were two, on the east and west sides of town. This led to, among other things, the town’s great high-school sports rivalry.
It was the same in Toronto. Grades 7 and 8 were at a “senior public” school, which might have been called a “junior high” or “middle school” elsewhere. For all intents and purposes, it was the same in all but name.
We didn’t have public school Kindergarten when I was growing up.
Elementary school was 1st-7th grades.
High school was 8th - 12th grades.
The absurdity of being a 13 year old boy with raging hormones in a school with nearly adult 17 year old girls was exacerbated by the fact that 8th grade was also referred to ‘subfreshmen’ class. Yes, that’s right, we were called ‘subbies’. Truly ridiculous system.
Ours is currently K-5, 6-8 (middle school) and 9-12. Except for one school in our district which is K-8.
I say currently because it could change based off demographics at any time. If they can fit more people in the elementary schools and need more room in the high schools - we will go back to Junior High and have 7-9 in the Junior High.
I know one district in Minnesota that for a while had 9-10 and 11-12 in different schools (White Bear in the late 80s).
SOMETIMES how they divide school has to do with educational theory. Frequently, it has to do with best use of facilities as the population of the district shifts. There is a point where you can’t fit K-6 in the elementary schools without 35 kids in a classroom, and you have to figure out how to shift the kids to fit them into existing facilities. Sometimes, you can make room in the high school by shifting grades.
Here is a little history on one room school houses in Minnesota. One Room Schoolhouses Closed – On ‘This Date In Central Minnesota History’ And the last one room schoolhouse in the state: Northwest Angle School HomePage I can’t tell if they still had high schoolers going there - I know ten years ago they did - Its hard to get to the high school in Warroad in the Winter from the NW Angle.
In the 60’s and early 70’s the school systems seemed to go through a lot of changes here is VA.
I went to an elementary school that had grades 1-5 but they started bussing during my 5th grade and that required me to be sent across town to a different elementary school that only had 4th and 5th grades.
6th and 7th grades I went a middle school that had previously been an all black elementary school. The facilities were horrible - “separate but equal” was clearly not equal. Integration caused a lot resuffling of students.
In 8th grade I was shipped to a 8-12 high school. Mixing 8th graders with older, huger students didn’t go well for us young kids. The locker rooms in gym class were a nightmare.
For 9th I was bussed the other direction to a brand new junior high for only grades 8-9.
Finally, my parents moved us right across form the high school they wanted us to go to and I got 3 years at the same place, a normal 10-12 high school. Unfortunately the school was so overcrowded we had to so split shifts. 10th grade was from 10 am to 4 pm so we couldn’t even do after school activities.
If I remember correctly, kids moved between classrooms, several times every day. The first and last room of the day was “home room,” and we had different classrooms and teachers for reading, science, math, and not sure what else. I remember phys ed in the “multi-purpose room” which everyone called the “gym” but we also ate lunch there, but I don’t remember whether that was daily or an occasional detour from home room or something.
The change in some areas from junior high schools to middle schools was not merely a matter of a name. There was a definite “middle school” philosophy that underpinned those changes, a philosophy that came out of the 60’s and 70’s zeitgeist that suggested that children in school were, in fact, people. So there was a concerted effort at personalizing and humanizing the 6-8 experience. (Yes, yes, in some places it was 7-8, some 7-9, and others 5-8, but those differences were insignificant.) One hallmark of middle schools was the team approach, in which a group of (usually 3-5) teachers would be responsible for a large team of kids. In the best of these, teachers had the flexibility to regroup kids and to modify the length of a class period, so that there was some very focused and elaborate grouping and scheduling. This was to redound to the benefit of all, and frequently did, particularly when the surrounding community bought in. This system also broke into the widening problem of tracking students, often begun in junior high and continuing into high school. So there were academic as well as social aspects to the change to middle schools. Some communities didn’t buy it, some did. Some middle schools were named that but in fact functioned no differently from the junior highs they started life as.
This is what I thought when I learned that my HS, which was only the last three years when I was there, had the added ninth grade. I was there it seemed as though most or all of the rooms were in use nearly all the time, so that if they had added ninth grade, it must been because of demographic changes. It wasn’t until some time later that I learned it was a national trend, and one that I thoroughly approve of. I remember it was a bit daunting when I arrived as a little seventh grader and all these ninth graders towered over me, even though the fact is they rarely if ever bothered me. In our school seventh graders were called “scrubs” and were suitable objects of “scrubbing”, namely the application of a hard noogie rub to the top of the head. I think it happened to me once. Nevertheless, when finishing elementary school it was pretty common for the sixth graders to commiserate and warn each other not to “let the A9s get you” the following Fall.
This is similar to how it was in my small town in the 50’s - 70’s. It was driven by population. There was a grades 1-8 Catholic school, a k-8 elementary school and a high school. As the population of children increased due to the baby boom, and Catholic enrollment declined (I think because of affordability) the need for another school arose so a middle school (grades 5-8) was built. I was in the first 5th grade class to attend the new middle school in 1971. And the Catholic school went to 1-4 a few years after that.
Now, in that same town, enrollment is declining due to the baby boom being over and people moving to larger surrounding towns, I think they’re closing the elementary school (because it’s older) and having the newer middle school building house grades k-8.
Perhaps what happened in my town will help explain.
The schools had been small schools scattered around the town where all grades were taught in one room. About 100 years ago they decided to consolidate into fewer centralized schools to reduce staff and expenses.
Around 1950 the University decided to open a High School run by the School of Education, taking students from all the surrounding towns. The towns adopted a model where Elementary was 1-6, then Junior High for 7-9, and the High School for 10-12.
Most towns nearby kept that model, but ours changed. Our population was booming, and soon outstripped the size of the elementary schools, plus they wanted to add Kindergarten. Faced with the need to build several new elementary schools to handled the students, they decided instead to build a “Middle School”.
By moving the 5th and 6th graders out of the Elementary schools, they could make room for the Kindergartens and population growth and only add one Elementary school. Better still, if properly designed the Middle School could become a High School should the population go back down.
Just to throw in my experience, which has since changed after schools have since closed.
We had:
Elementary: K-4
Middle: 5-6
Junior: 7-8
High: 9-12
In my part of town (west), the two schools I went to closed and consolidated into 1 school, so now it’s a “Middle/Junior 5-8” school" but other parts of town still follow the 4 school system as far as I know, which may change as a newer junior high is being built on the eastern part of town which may again cosolidated more schools, not sure.
Same thing in the City of Buffalo and for most private and Catholic schools in the area - most are K-8 and 9-12. The suburban districts have middle schools - 5-8 or 6-8 between K-5 and 9-12. Old money private schools are straight K-12.