I'm really confused by this just because even when I was in Junior High, backpacks weren't allowed to be brought from class to class. That was back when our Junior High was 3 floors & it was quite possible you could have your locker on the 3rd floor and class on the 1st floor & you did have to run in-between each class to your locker to get books & things. The only time we had our purses were at lunchtime otherwise they were in the lockers too.
Let's see I was in Junior High way back when -- It was the election between Ronald Reagan and Jimmy Carter happened when I was there because we did a mock election -- so whatever year that was -- I don't feel like calculating it out.
My DD's Middle School does team centers -- they have it *so* easy -- they have lockers in one set and around that group of lockers are their core subjects in a U type thing. The *only* time she leaves her little area is gym, lunch & choir. They aren't allowed to bring backpacks to classes either.
We never were allowed to carry our backpacks to classes in High School either. So, at least around here, this is not a new concept of taking your backpack to school & putting it in your locker for the day (I don't remember carrying my purse around school either even in HS -- it was in the locker too).
That's how it's always been, I don't know when it changed to people carrying backpacks to class (or if it ever did around here) and then went back to them having to be in their lockers.