When most of these guys were in their early teens, getting an A in history or math was far less important than earning $5,000 mowing lawns over the summer.
In my experience, most boys are simply bored with school and would be better off doing something more interesting (and more productive, in the long run) with their time.
The irony of this story is amazing -- girls have become more dominant in the American classroom at the same time the quality of American education has declined considerably.
However, when I went to public school, beginning in about grade 5, we turned our attention increasingly to things of practical significance (math, science, wood and metal shop, etc) in preparation for becoming Masters of the Universe.
When my sons went to public high school, most practical matters seemed to have disappeared from the curriculum. High school juniors are now treated like third-graders, and it is not surprising that girls, who have always "ruled" third grade now rule high school as well (at a time in their lives when they have other advantages over boys).
"Boyness" does not lend itself to "soft" regimentation, which is now the purpose of public education.