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 Monday Flying 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)