Being only the third in the series, Carry On Teacher lacks a few of the elements associated with the films, but we can already see a rough blueprint of how they will develop.
William Wakefield (played by Ted Ray, in his only Carry On film) is the Headmaster of Maudlin Street Secondary Modern School. His hopes of getting a job at a shiny new school rest entirely on the results of a visit by Government Inspector Miss Wheeler, and noted child psychiatrist Alistair Grigg (Leslie Phillips). However, the pupils don't want Wakefield to leave, and plot to sabotage the inspection by any means necessary.
Several actors would go on to be Carry On regulars and here seem to be rehearsing the roles they would play on a more regular basis, with Kenneth Connor as an affable duffer, Charles Hawtrey as a camp neurotic, and Joan Sims as Sarah Allcock, the object of male desire. The exception is Kenneth Williams, playing straight as Edwin Milton, the English teacher, very different from the leering grotesque persona of the later films. (Look also for a very young Richard O'Sullivan, of later Man About the House fame)
Being a Carry On film, some of the script revolves around sex, particularly Grigg chasing after Allcock, and the innuendo in her name does not go unnoticed. However, this is rather tame and anodyne, lacking the bawdy energy that the likes of Sid James would bring into later films of the series.
In fact, the world of Carry On Teacher is an uncomplicated, sometimes sentimental one, but modern viewers might find one aspect jarring. Corporal punishment is a recurring theme, particularly the reluctance of Wakefield to administer it, and is a reminder of a time when British school children faced the possibility of physical punishment from their teachers.