They weren’t - when I was young, boys used something like this and girls used something more like a tote bag. Backpacks were strictly for hiking.
That was one of the shibboleths for rail fans. There was a locomotive works there and ‘bean’ or ‘Peru’ told you how much studying they had done.
Some kids I went to junior high with carried books in an open top canvas bag with shoulder straps. Technically a backpack, but not in the way we think of it today. More like a shopping bag with shoulder straps.
I have never been able to study from a Ebook. Casually reading fiction 
on a Kindle is relaxing. Studying from a Ebook breaks my concentration.
I just bought a book on ***Python for a online class that starts July 8. I think it’s available in Ebook. But I need a real book to read and study. My yellow highlighter near by and ready to use.
Gosh, I’d be in serious trouble in todays high schools. I tried to finish my homework in study hall. Leave my textbooks in my locker. I took them home to study before tests.
*** Bill Lubanovic Introducing Python
Excuse me, I meant May 20th.
A relative of mine was one of, I think four, co-authors of a quite successful textbook (high school level, not college) and the royalties were sufficient for them to buy land in the countryside and build a very nice house on it. (A prospect that would have been entirely unattainable on a teacher’s salary.)
I started high school with a Satchel. similar to a ‘messenger bag’. Classic English school bag, and still in use in Aus in the early 70’s. By the late 70’s, I remember something more like a bowling bag or a sports bag, and now, backpacks.
We had no lockers in elementary school in Aus or Arizona, lockers in high school, and lockers in 1 of 4 Melbourne universities I had contact with – the Institute of Tech. High schools still have lockers.
OTOH, my mother wrote quite a few ESL (English as a second language) high school textbooks, but she she was working as a salaried employee of the publisher, and never saw a cent in royalties. I suspect that her case is more common than yours.
My professor for optics in my EE program had us use a test book he wrote. He gave each of us back $5 as that was his royalty.
This was back in the 80s.
I would imagine high school books sell thousands of times more than EE books.
I’m sure her publisher got plenty. She herself wrote under a pseudonym, which she didn’t have any rights to.
I’ve also heard of unethical professors who would write their own text, steeply overprice it, and then set it as the required book for their courses, just to milk more money out of the students.
On the other end, I had a course where the professor wrote the book, and he had it for sale at cost (using the cheapest binding etc.) in the bookstore.
Was the binding so cheap that the book fell apart by the end of the semester, so the next semester’s students couldn’t buy used books? Clever professor!
Selling at cost makes it hard to make it up on the volume.
It was only something like $5, so buying used wouldn’t have made much difference. And by “cheapest binding”, I mean the sort that if it came apart, you would just put the binding back on: One of those plastic things like a student might have used for a long term paper.
I had a computer science PL1 book written by two Professors at the University. It was being prepped for publishing. Students were told copies were available for purchase at Kinkos. Plain cover with spiral binding.
We helped proofread that book. I know students did the same thing in two other semesters.
I don’t know if it ever got published. I never saw it in the campus bookstore.
Me too (UK).
A Satchel (not mine)
but I spilled ink inside it. (we had fountain pens for a very brief period in 1967, but I’ve rarely if ever seen them since that date). After that I used a duffel bag, as far as I can recall.
One of the guys I worked with had bitter memories about being forced to use a dip pen, to “write lines” in England in that period.
Many countries had that (which still do?) I suppose the theory is that if a kid can write legibly with a dip pen, they can write with anything.
It’s now rare for dip pens to be used for anything except artistic uses.
That is why they were forced to use fountain pens. And “writing lines” had, to some extent, the same justification. The dip pen was just punishment, and intentionally kind of arbitrary, in the same was as military punishment: the arbitrariness is part of the punishment.
Dip pens are more likely to blot, particularly when some other student has put blotting paper in the inkwell, which sticks to the nib and carries ink. Then you have to start over.
He was still a bitter about it years later.