A new teacher, Dr. Dr. Bach, is transferred from his quiet village elementary school to the Mommsen Gymnasium, bringing along his nephew Jan. Bach's lackadaisical methods raise the suspicions of the other teachers.

Pepe Nietnagel and his fellow students of the Mommsen school come up with all kinds of ideas to get out of doing any actual school work. This includes simulating suicides, setting off the air-raid sirens and abusing the school director's new broadcasting system. They succeed in sending their teacher to a sanatorium and get a replacement that turns out to not be so bad after all.

Pepe Notnagel (who inexplicably had his name changed from the first movie's Nietnagel) and his classmates scheme to get around doing any actual school work by cheating or sending their teachers to the sanatorium. A Swiss documentary film maker disguises himself as his brother in law, who got a position as an exchange teacher, to aid his project of making a movie about the current youth.

Mommsen Gymnasium director Taft secretly places his nephew as a spy with the difficult class of Pepe Nietnagel. During the celebration for the 100th anniversary, a simulated fire forces the school to shut down for a week. The director's attempt to get a tough teacher assigned by the department of education results in the exact opposite because of Nietnagel's intervention.

Due to a plot by the teaching staff, headmaster Taft is forced into early retirement and Knörz is appointed headmaster. However, they didn't count on class 13a, and especially not on their spokesperson Pepe Nietnagel. They are anything but happy about losing Taft, their favorite enemy. Without further ado, Pepe and his friends join forces with Taft and hatch a series of daring pranks to get back at Knörz.

Pepe Nietnagel's father has a valuable stamp collection stolen in Amsterdam. Street musician Pit recovers it. To show his gratitude, Pit is invited to Baden Baden and enters the Mommsen Gymnasium. There, he joins Pepe in his pranks.

Principal Gottlieb Taft's twin brother Gotthold Taft partakes in the most recent prank by faking his death and promising a large inheritance to the Mommsen-Gymnasium and the principal. Of course, the inheritance is tied to many embarrassing conditions.