It was the dead mouse in the jar of gobstoppers that turned an early Roald Dahl Day celebration into a tale of the unexpected for Lesley Walker.

Mrs Walker, who teaches English at Hatch End high school, Buckinghamshire, brought her keenest Year 8 and 9 readers to the Roald Dahl Museum and Story Centre in Great Missenden, the author’s home village, to thank them for their work on Readathon, the annual schools sponsored reading event that supports the Roald Dahl Foundation. The museum will host a weekend of celebrations on September 16 and 17: Roald Dahl Day itself is on September 13, which would have been Dahl’s 90th birthday (he died in 1990). One of the galleries is devoted to the great man’s childhood, hence the gross gobstopper display (the mouse is a fake but, this being a centre for all things Dahl, it looks horribly real) in homage to “The Great Mouse Plot”.

This is a chapter in Boy, his first autobiographical book, in which he describes a war of attrition with a sweet shop owner who has elements of Miss Trunchbull crossed with the Witches.

For Mrs Walker, it means only one thing: “I’ve used that piece for a comprehension.” She is a committed Dahl fan, like Sulaiman Meher in Year 8 who loves George’s Marvellous Medicine, “especially that bit where his mum takes him to a dentist but this guy takes his tonsils out”, and school librarian Louis Victor, one of Dahl’s first generation of child readers. “I was in primary school when Charlie and the Chocolate Factory came out. He dared to put horrible ideas into children’s books at a time when most of them seemed a bit too cosy.” His Norwegian roots show, Mrs Walker says, in the ghastly villains and their gruesome ends. “His witches are in the tradition of Norse tales, really quite nasty.”

But Mr Nasty is encouraging to writers of all ages, especially procrastinating ones: he didn’t publish Charlie and the Chocolate Factory, his breakthrough children’s book, until he was 47; he kept some ideas in notebooks for 20 years before using them (including the storyline for Matilda) and didn’t care about neat handwriting. Activities in the Story Centre are intended, says director Amelia Foster, “to get children doing creative writing without realising they’re doing it”. The appeal of composing with fridge magnets, capturing dreams in Dahlesque dream bottles and exploring a replica of Dahl’s writing hut (he told children that wolves lived in the real one, to keep them out) endures well into secondary school, as the Hatch End party can testify.

Last year the school raised pound;2,600, making a total of pound;10,000 over four years for Readathon (which shares proceeds between the children’s cancer charity CLIC Sargent and the Roald Dahl Foundation’s projects related to neurology, haematology and literacy). Mrs Walker runs Readathon the week after October half-term, and encourages “random acts of reading”:

“The children in the lower school (Years 8 and 9 at Hatch End) can read in every English lesson. The teachers talk about their own ‘desert island books’ so that they can see that we read too. We bring in authors and performance poets. There is an air of competition and the boys love it.”