GCSE pupils are reading books better suited to youngsters that are three years younger, according to a study.
It argues that many secondary school pupils are not reading challenging enough books for their age group.
The annual study, published by assessment service Renaissance UK, is based on an analysis of the reading habits of almost one million UK schoolchildren, with youngsters quizzed on what they have read.
It uses a formula to calculate the difficulty of a book based on factors such as sentence and word length.
It found that average book difficulty rises as pupils get older, with primary school pupils reading books that are more advanced for their age.
But this starts to fall in secondary schools, with pupils in Year 7 – those aged 11 and 12 – reading books that are around a year less than their chronological age.
By the time they are in their second year, Year 8, they are reading books two years behind their actual age.
And those in Years 9 to 11 (aged 13 to 16) were reading books at least three years below their chronological age, the report says. This age group covers those sitting their GCSEs.
“Children consistently read above their chronological age throughout primary school, and non-fiction difficulty has risen dramatically,” the report says.
It also notes: “Book difficulty drops off sharply in Year 7, with secondary students consistently reading behind their chronological age.”
Professor Keith Topping of Dundee University, who carried out the research, said: “To avert a further slide in literacy levels in secondary schools, pupils should be encouraged to push themselves to read more difficult books.
“By their teenage years pupils are more likely to take advice from their friends and peers than their teachers and parents about the types of books they should be reading.
“With this in mind, teachers could encourage them to talk more openly about what they are reading and make appropriate suggestions to their classmates.”
Renaissance UK managing director Dirk Foch said: “The fall in teenagers’ reading ages is striking.
“By the time many come to sit their GCSEs, many will have a reading age of 13 or less, meaning that they could even struggle to comprehend their exam papers. This could have a significant impact on their future academic success.”