Unman, Wittering and Zigo (1971)

Fed up with the frantic world of advertising, former advertising executive John Ebony takes up a position as a teacher at Chantry, a public boarding school for boys. Eager to fill in for his unfortunate predecessor and educate the next generation of pupils, the unsuspecting first-time instructor is shocked to discover that his efforts to exercise authority have the exact opposite effect of what was intended. Then the seemingly-respectful but devilishly manipulative teenagers of Class Lower 5B drop a bombshell, and Ebony starts fearing for his life. It's evident that the unruly students have the upper hand, plus he's dealing with a pompous headmaster and a disbelieving wife. How can he cope--and survive?