What you said at the end, there, was something I was going to point out...because of the reality that some girls and boys may have unique disabilities (often undiagnosed), what you're proposing simply wouldn't work.

It also ignores or marginalizes the presence of nonbinary (yes, I understand you said you weren't originally referring to them) and transgender students, while potentially stigmatizing gay, lesbian, and bisexual students (even those who are cisgender).