In this term, it didn't just saying about public school. There are some school that not in the standard public school curriculum. These type of school usually are for the practical purposes of students. The practical purposes are want to enhance creativity, skills, practical knowledge, experience so that if the students graduated, They could enter a work site or company that require experience the most. They didn't need to go to college or University to do this.
The Skills that have been taught there must be differ, because of the different skills that mostly woman's or man's interests.
For example : School of Sewing, flower arrange, etc
I think children need to be with people of the opposite gender as that's life and when you grow up you won't be separated. So it's better to get to used to it when your younger so when your older it's normal to you and also so when you find 'the one' your ready and its not awkward.
No one benefits much from this and there have been times when it has been found to be against the law. (1) It also doesn't help because people need to learn interact with folks of different genders. This is an important part of real education. Keep genders together!