The biological makeup of men vs. women is a lot more distinct than a one race vs another.
Firstly, there is the most obvious: sex organs and growth. Erections, ejaculation, periods, breast/hip growth, etc. are all sensitive topics, and I have not seen evidence that keeping these topics sensitive is a bad thing. Girls generally hit puberty earlier than boys, so it doesn't really make sense for 12 year old boys and 12 year old girls to be grouped together in certain situations, when girls are having a sexual awakening and boys aren't (as a cohort - obviously everyone hits puberty at different times, but society functions through generalizations).
Secondly, there is the general impact of hormonal differences. Hormonal differences have a striking impact on emotional development, and that needs to be considered when raising children.
Biologically, the only general difference between a black boy and a white boy is their skin color, which at an individual level makes no difference at all to their development. Obviously if society treats these skin colors differently and that impacts development, that is another issue entirely and should be handled separately from any gender issues.