The Belles of St Trinian's

The Belles of St Trinian's is a 1954 British comedy film, directed by Frank Launder, co-written by Launder and Sidney Gilliat, and starring Alastair Sim, Joyce Grenfell, George Cole, Hermione Baddeley. Inspired by British cartoonist Ronald Searle's St Trinian's School comic strips, the film focuses on students and teachers of the fictional school, dealing with attempts to shut it down while the headmistress faces financial troubles, which culminates in students thwarting a scheme involving a racehorse.

Synopsis from Wikipedia, CC BY-SA 4.0. Everything below written here.

Poster © the film's rights holders.