Ronald Searle was one of Britain's best-loved cartoonists, and Geoffrey Willans (if I remember correctly) a former teacher. If there is such a thing as a genius, then Willans and Searle together were one.
The Molesworth books purport to be instructional manuals by an English public schoolboy named Nigel Molesworth, about how to survive the school experience. From the day the first was published in 1953, they became a wild success, especially with schoolchildren. They are still in print and still eminently applicable (which says something both about the quality of the books, and about the nature of the British school system, which even at that point hadn't changed much in 400 years).
The wild misspelling that permeates them caused hysteria among parents, and their removal from many school libraries (the books, not the parents). Nevertheless, many phrases from them have since gone into the English lexicon, particularly "enuff said" and "as any fule kno".
The quartet consists of:
Down with SkoolHow to be ToppWhizz for AtommsBack in the Jug Aganeand an omnibus edition,
The Compleet Molesworth, reprinted by Penguin as
MolesworthThese are considered absolute classics in the UK along with gems such as
1066 and all that. Whether they're intelligible to anyone but Britons is another matter; but I didn't think Monty Python would be, and I was wrong about that...
P.S. And should you be wondering (during reading) exactly what Treens might be, they're the myrmidons of that most unforgettable villain The Mekon (whose portrait you can see
here), from the wonderful contemporary comic-book series
Dan Dare.