OK, for a bit of back story to this infamous work. Though this was not his first, this particular manga was the first success for the infamous veteran manga artist, Go Nagai. Before this, Nagai had been working as an assistant for manga legend Shotaro Ishinomori (creator of Kamen Rider). However, on the side Nagai had been publishing gag manga in various publications for about 6 years.
Then, early in 1968, Weekly Shonen Jump published the first installment of Harenchi Gakuen (Shameless School)........and the manga world would never be the same again......
As for the story of this manga.......well, it IS gag manga, so alot of the plots are indeed formulaic (the curse of gag manga, I'm afraid).
Basically, the series more or less is biting satire of the dehumanizing effects of Japan's monolithic education system in the 60s and 70s. It more or less involved the day to day antics of the dough-eyed delinquent students and there utterly bizarre teachers, who are all conpsiring to either get licquored up or to see women in various states of nakedness.........unless they're women, in which case they lost there clothing at a drop of a hat in order to get there way.
The school was filled with a whole host of bizarre and eccentric characters. This wholly confusing host included such characters as "Bearded Godzilla", a caveman-like character who wears a flimsy tiger skin that exposes his lower half. Then there's the gym teacher, who wears absolutely nothing but one well placed gym shoe. 0_o
And then, there was the ending to the series......one of the best in manga in my opinion. The final volume of the manga told a long story about a FULL-ON WAR between the school and the PTA, with guns, planes, tanks, and bombs. Everyone in the manga died horribly.
This was, of course, a reference to the problems that Nagai and Shonen Jump were facing from parent's groups. Keep in mind that, even though things like nudity, toilet humor and sex jokes are common in shonen manga today, in the late 60s it was COMPLETELY unheard of. Nagai was the absolute first to do this, and because of this he became the target for a MASSIVE anti-obscenity campaign in Japan. Copies of Harenchi Gakuen were publicly burn in city squares. It would be the main target for several years after......that is, until the publication of Fist of the North Star.
But, like they say, no publicity is bad publicity.

Today, this manga's influence cannot be measured. No less a person as Osamu Tezuka himself said that, because of Nagai, the taboos that had previously been put on children's comics in Japan were COMPLETELY destroyed, opening the flood gates for a host of imitators and tributes.
Since then, every manga that has been released in Japan has been at least SOMEWHAT influenced by Harenchi Gakuen. One of the most famous users of the Nagai formula -toilet humor, sex, eccentric characters- is Akira Toriyama, whose own Wonder Island and Dr. Slump were both heavily influenced by Nagai. HighSchool Kimengumi is also a good example.
Even today, the humor in Harenchi Gakuen is still effective, a good sign of how ahead of its time it truly was. It has never been released in English, however, if you can ever get a copy, please still read it. The imagery alone is enough to inspire a good laugh.
