Cacao - Shuukatsu!

The protagonist, due to his fear of young girls, aims to be an all-boys school's teacher. But because one of his relatives' recommendation he is assigned to an all-girls school instead. However, he becomes quite popular in the class.
At his school, there is a legend among the students. If two people manages to do the business on the field trip, they will be happy together forever. And there're several girls who are interested in the protagonist.

And thus, the much-anticipated field trip begins.

[Edited from: Official Site]