Human beings are sexually dimorphic, but most of the advantages or disadvantages are negligible or can be overcome with training, so it makes little difference. It makes even less difference in middle and high school aged children, since everyone is at (somewhat) different points developmentally anyway.

Fun fact: the studio made the movie dogshit, too. Watch the trailer for it - they filmed a bunch of scenes from the book, including the original ending, that never made it to theaters but still ended up in the trailer.