Boys choose to read less challenging books than girls and this gets more pronounced as they get older, according to a UK-wide survey of reading habits.
The study of 100,000 five to 16-year-olds found for most age groups the difficulty of books chosen by girls was "far ahead" of those chosen by boys.
But boys are reading as many books as girls, said Professor Keith Topping who headed the report.
He called for better monitoring of what children are reading.
The gap in reading standards between boys and girls was most marked between the ages of 13 and 16, with the favourite girls' book for that age group being the vampire tale Twilight, by Stephenie Meyer.
This was rated as more difficult than the boys' favourite, The Dark Never Hides by Peter Lancett.
High-achieving children - defined as reading two years above their age - are not challenging themselves enough when it comes to reading as they tend to opt for easier books than their reading ability warrants, the report suggests.
Harry Potter author JK Rowling dropped down the top 10 list of most popular children's authors, from second to ninth place, compared with a similar survey of reading habits conducted two years ago.
Prof Topping, of Dundee University, said: "It may be that boys have read the whole of the JK Rowling novels and there are no more to read."
While he said Stephenie Meyer was a "rising star" among children's favourite authors, Roald Dahl remained the most popular.
"He remains relevant to a wide range of children and remains popular with boys and girls which helps make him come out top," he said.
Given the survey findings he said there needed to be closer monitoring of what children are reading.
"If they [children] are reading books that are below their independent reading level it may give them enjoyment but it won't extend their reading ability and literacy rates are at risk of continuing to decline," he said.
The children's reading habits were confirmed by online quizzes taken on the books they had read.
The findings contradict those of a similar survey two years ago which found boys were opting for harder-to-read books than girls.
But Prof Topping said that survey dealt with a much smaller number of children so the latest one may be more accurate.
The report was commissioned by Renaissance Learning, which pioneers reading tests widely in use in the US.