The author of How to Train Your Dragon has criticised an "obsession with grades" and "literacy modules" in today's education system.
Cressida Cowell's series has sold eight million copies around the world, and has been adapted into movies and a TV series by DreamWorks.
The writer and illustrator said that, at her school, "there were no grammar lessons and I went to a very English-pushy, all girls' school".
She told the Press Association that modern pupils were suffering because education ministers "want everything to be measured all the time" and "we've become obsessed with grades".
She said: "It's reading for pleasure that makes the big difference to children's later education. School is so off-putting. It's all about the literacy modules."
Cowell wants pupils to be able to write, once a week, whatever they want to, saying she benefited from a similar experience.
"My spelling wasn't very good. My handwriting was pretty grubby," she recalled.
"It was messy. It was not full of 'wow' words. It was not beautifully written. But I was learning the joy of writing and that's what I'm doing now."
She criticised ministers for being obsessed with "short-term goals" and added: "It's very difficult to mark children's creativity and enjoyment."
Cowell, whose new The Wizards Of Once series has also proved a big hit, wrote stories as a child while on holiday on a small, uninhabited island off the west coast of Scotland, without TV or electricity.
"I worry about children's lack of contact with nature," she said.
"Children need to be wild. Something is lost."
Twice Magic is the second book in Cowell's The Wizards Of Once series and is published on 20 September.
School standards minister Nick Gibb said: “To be able to express themselves, children need first of all to be able to read and write, which are the foundations of a broad and balanced education.
"Our reformed English language and literature curriculum encourages children to read widely, and our increased focus on phonics means more children are mastering the basic skill of reading in the first years of school.”