Every single word in more than 33,000 books for children and young people has been scanned and the data used to provide reading ratings for each text, according to a level of difficulty from 0 (lowest) to 13 (highest).

“We can tell you average sentence length and we can tell you the most difficult word in a book and how many times that word is used,” says James Bell, director of professional services at Renaissance UK, which carried out the research.

The ‘hardest and easiest’ children’s books

The results of the research:

• Of all the books researched, Bad Bat by Laura Hambleton and No, Sid, No! by Kate Scott both have the lowest level of 0.2

• Gulliver’s Travels (unabridged) has the highest level of 13.5

• Mr Greedy by Roger Hargreaves at 4.4 is higher than some Roald Dahl texts, which has caused surprise in some schools. 

• John Steinbeck novels The Grapes of Wrath and Of Mice and Men are 4.9 and 4.6 respectively

• Me Before You by Jojo Moyes (Richard & Judy Book Club recommendation) and LEGO Star Wars: Into Battle! both have a level of 6.8.

Mr Bell said the Harry Potter series starts at around level 4 but moves to around 7 as JK Rowling “developed her audiences”. Dr Seuss’ works were also among the easiest texts (at 0.5) while Ivanhoe and Don Quixote are among the hardest texts at around 12 and 13, said Mr Bell.

The research was conducted by psychometricians and statisticians working for Renaissance UK.