|Entitled "Kyou no Go no Ni"
This one-volume manga by Sakuraba Koharu portrays the fifth grade in a... different light. The chapters ran in Young Magazine, a relatively small publication, and were then released in volume form, when it gained some cult following.
What makes this manga particularly unique is not it`s characters, which represent fairly run-of-the-mill manga personalities like those found in FLCL, Azumanga, and even Sister Princess--which should give you a pretty good idea of what does make this manga interesting: the perfect blend of school humor, plain ridiculousness, and raging sexual innuendo.
Ah, fifth grade like you wish you remembered it!