Schools are not sexist; they fail both genders.
They are inherently sexist. At least the ones here in the US.
It used to be, back in the dark ages when I went to school, that girls were not encouraged in the STEM fields. This has definitely improved as women have pushed their way into many places once deemed inappropriate or impossible for women, and they proved their worth. There are very few teachers left today who have the bias that only males can excel in math, science and technology. The sciences, especially, have many more women than 50 years ago. Technology, not so much, yet.
I disagree that the schools are inherently sexist. No more than the underlying sexist biases of our culture generally.
So you have particular examples?