Belles of St. Trinian's was the first of several British comedies inspired by the fear-inspiring girl's school created by cartoonist Ronald Searle. The girls of St. Trinian's aim their deviltry at a gang of crooks who plan to steal a famous race horse. Alastair Sim wraps up the proceedings with his dual portrayal of the school's severe headmistress (!) and her bookmaking twin brother. Also worth watching is veteran supporting player George Cole, who makes a tidy profit on the alcoholic beverages produced in the girls' science lab, and toothy Joyce Grenfell as a diligent lady constable. Like most of the subsequent "St. Trinian's" farces, Belles of St. Trinian's was a joint effort of the producer/director/writer team of Frank Launder and Sidney Gilliat.
~ Hal Erickson, All Movie Guide