Sakura Machizaka Stories Vol. 2 "Sensei ga Oshiete Ageru!"

Main character is a popular student, but with poor grades. He will need to stay for another year if he fails next exam, so he is sent to the summer study camp. But the four hellish teachers there turn out to be small girls with superior academic abilities fit for university already. After all, this summer is going to be fun.

[From vndbreview]