If you're not a fan of the great Mr Hay, have never seen one of his films but are wondering what all the fuss was about don't watch this one first. Eventually you love this but only after you've become a fan. To do that watch OH MR PORTER first, then you'll be desperate to voraciously devour this and the rest of them.
This film basically showcased the music hall act Will Hay had been touring with since the 1920s, his performance is therefore honed to perfection. To some extent this is like the pilot episode of what was to follow - it's nearly there but even so however many times you watch it, it never gets stale or fails to make you laugh. His character and his story is extraordinarily silly but by setting it within an insular and isolated environment, without contextual reference to the outside world, such silliness seems fine. English public school system in the 1930s was hardly the exam-focussed institutions of today. They had improved since the bad old days when they were there to make money and in theory develop boys' character rather than educate him with the philosophy exemplified by the famous quotation of Thucydides: The strong do what they can and the weak suffer as they must but a lot of them were still atrocious places with completely unqualified teachers so Narkover School is probably a lot more representative of reality than you'd imagine. This is hardly a brutal and cutting satire of that system but nevertheless like Monty Python did years later (who'd also had first-hand experience of public schools) it laughs at the stupidity and incompetence of such institutions.
Will Hay was born for cinema. Although he had been a massive comedy star on the stage since starting off as 'the English W C Fields' in the 20s, because so much of his humour is derived from his facial expressions and his incoherent mumblings - things which couldn't be picked up on a stage fifty metres away, moving and talking pictures were the perfect medium for bringing his anarchic yet safe humour to the world. His first few films at BIP can be ignored but having moved studios to Gaumont-British, this was his first 'proper' picture. Some might say that all his subsequent ones at G-B were just remakes of this, indeed Will Hay himself thought that towards the end of his contract there but if it's such a good formula, why not repeat it! As time progressed his pictures got much better both funnier and better produced but this one, the original is the comedy equivalent to the source of the Amazon - perhaps not as wild and torrential as further downstream but pure and full of life.