Little bit of history off the cuff. Please remember the numbers I use are approximate from what I remember at the time.
Charleston High School was one of those Kindergarten through High school situations. Pretty much all the enrollment come from Charleston itself with a few from the outskirts. The school typically carried around 300 to 500 students.
Bradley was then one of the largest high schools in the state, with enrolment generally around 2,000 plus. in 1977 it was like 2100 students and before they moved the 9th grade to the middle schools it hit 2400. (My freshmen class started with 600+ students).
Cleveland High at the time had around 1000 to 1200 students as best I can remember.
So, when they built Walker Valley, they did away with Charleston High School, in favor of a new name and all that entails. I thought it was a bit of slap in the face of the Charleston legacy which while not great did have some good history. And Walker Valley still tries to embrace the names of the players but avoids the "Charleston name tag" history. (I thought why not keep the name of the Panthers but what do I know).
But the upshot was that the county had and has open enrollment. You can go to either HS in the county, but the feeder of Walker Valley is supposedly Ocoee Middle and the feeder to Bradley is now Lake Forest (formerly Trewhitt) Middle School.
So essentially, they took in Charleston High School (there is still Charleston Elementary on the original campus and the football field and stands still exist) and split the student population of Bradley when creating Walker Valley.
Because of the growth Cleveland High is now the largest school in the county, since they split Bradley with Walker Valley. Bradley is now a small 6A school and Walker Valley a large 5A school with Cleveland 6A.