The theory, as Fred mentioned, among many feminist-oriented teachers is that boys and girls are psychologically i.e. mentally the same. The long and short of it is: we’re not. When I was in grade school, I could barely stand the boredom. In the eighth grade the nun made me write a note to my parents that I wasn’t paying attention in class. I wasn’t. Guilty as charged. Did I care? Not much. The only thing I liked about grade school was recess and the school library. I’m positive if they’d had Ritalin in those days (50’s and 60s), they would have drugged me. And a lot of other boys.
"They" had Ritalin and related pharmaceuticals well before the 1950's. What changed was the perception of what constitutes normal/acceptable behavior for boys.