The concept of gender in Japanese schools is very interesting. Particularly I've noticed that during events like assemblies, morning meetings, and even in most classes there is a separation between genders. In the first picture, you can see that in the classroom there are sets of two columns, one all boys, the other all girls. I can only imagine that this is to keep them more separated from their own gender peer groups, hopefully keeping their concentration more on learning and less on chatting during class. Outside of class, you can easily notice students in their peer groups, especially when arriving and departing school. Oftentimes students will walk along the road in pairs or groups of 3 or 4, but all the same gender, with occasional exceptions. I've also noticed this phenomenon at Iwate University. Although there are more exceptions, I would be comfortable saying that often students are with a group of their own gender. However, when eating there is a difference between college and middle school groupings. Middle school lunch is within the classroom, and so the desk organization stands. At Iwate University, lunch is eaten in a separate cafeteria building, where students of all genders intermingle, though there are still a lot of single gender groups.