Gakuen Ouji

Summary translated from the back cover:
The stage is set in the prestigious Private Joshi (girls) Oka High School — or more commonly known as Joshi High. It became co-educational a few years ago, but females still heavily outnumber the males. The number of males could be easily counted. While one would think males would be pampered in such a harem school, the reality is far from being heavenly. It is the world of female domination.
[Taken from Baka-Updates Manga]