Such a Boor (1934)

This is an earlier, much less successful version of the The Punch Bowl (1944), but the story is basically the same: The famous writer Hans Pfeiffer has problems in directing his latest play about a high-school class. He's told the reason is that he never attended a regular school, so he decides to swap roles with his younger brother Erich, who's a never-graduating, always kidding senior in a small-town high-school. When Erich aka Hans suddenly turns from class clown into the role model of a pupil, everyone believes it's just another prank. So Hans is practically forced to take over Erich's standard... and enjoys it.