I have never encountered a dress code that only set out standards for one sex. They are written for both sexes.
A proper, respectful environment is an education in itself! The environment reflects and encourages certain ideals.
What you wear changes behavior. Both the way you behave and the way you are treated. It is not insignificant it is part of a good education.
What girls and boys can learn from dress codes:
These might be the best lesson they learn all year.