Growing up they moved our district from 7-9th grade, which they called Junior High, to 7th & 8th, which they called Middle School. 9th graders got sent to high school. Tough transition for the 9th graders.
Something sort of similar happened in our schools when I was growing up
It was a growth problem more than anything
I started out in a school that was 1-6, in a brand new school, brand new suburb. It grew so fast by the time I got to 5th grade, we were sent to an old school that was reopened just to hold 6th grade
Then we went to a 7/8 grade Jr High
We had a really strange set up where our 9th grade was sent to another stand alone, old facility, only grade in the building. We were in limbo. We were the final year where 9th grade did not count towards High School credits. We weren't Jr High, we weren't Middle School. We weren't anything. We were just 9th grade.
The next year I went to the High School and started 10th Grade.
That same year they reorganized the structure so my old elementary school was just Grades 1-5
The school where I attended 9th grade was renamed a Middle School and was now Grades 6-8 (we no longer had Jr High)
My High School welcomed not only my 10th grade class but also a 9th grade class at the same time.