Getsuyoubi no Soratobu Orange.

Watermelons, orange-like alien teachers, and a dog named after fermented beans: these are the characters that show up in this lively and quirky world of Getsuyoubi no Soratobu Orange. Yoshino, the hyper one, will run till the end of the Earth. Tsuka-pon is the orange(?) professor. Natou is the dog. "Senpai" will usually be found sleeping or lost. Manaka loves animals and sports thick eyebrows. And last but not least: Nanami, a.k.a. Nacchan, will be found riding her bike to school. A cute and quirky world awaits for this lively cast!

(Source: MangaHelpers)