Two masked thieves burst into a classroom and threatened a 58-year-old teacher with a metal pole before making off with a briefcase full of end-of-term report cards.
A third teenager, known only as Zacharia, attempted to escape, but was caught on the school steps.
It was a plot worthy of a James Bond villain. Mastermind Zacharia persuaded two pair, aged 14 and 15, to swipe the report cards because he feared his poor marks would force him to repeat a year.
His henchmen, who did not attend the school, were released after police discovered they had an otherwise clean record. But Zacharia has been expelled from the school, although he will not be prosecuted.
Friends described the act as out-of-character, saying Zacharia was well-liked. But the headteacher, Rainer Hensen, said: "We must give a clear signal that we do not tolerate violence in our school."
The incident has provoked questions about Germany's tough school system, where pupils must repeat a year if they do badly.