Teenagers' reading skills are not good enough to understand a GCSE exam paper, a new study claims.
It suggests that on average, a student's reading age was around five years below that required for a GCSE exam.
The study, by educational software company Renaissance Learning, looked at the results of reading tests taken by around 24,500 pupils aged 14 to 16.
It then analysed the reading level required to understand a number of randomly selected GCSE exam papers and materials by using a programme which looked at average sentence length, word length, word difficulty level and and the number of words in a book or passage.
The study found the average reading age required for the exam papers was 15 years and seven months - approximately the right age for a teenager sitting their GCSE exams.
But the results of the reading tests showed that a teenager's actual average reading age was around 10 years and seven months - a gap of five years.
Dirk Foch, managing director of Renaissance Learning said the results were "alarming".
"By GCSE level, most educators make the basic assumption that students are able to read and comprehend an exam text. It's clear from this research that this is not a safe assumption to make.
"Most students have a reading age significantly below the level that GCSE texts are being aimed at meaning some students are not only failing to access the curriculum, but they are failing to comprehend key course and exam texts."
A Department for Education spokeswoman said: "For far too long, too many children have not been reaching the expected levels of reading at a young age, have not caught up, and have then struggled in secondary school and beyond.
"That is why we are prioritising the teaching of systematic synthetic phonics in primary schools as the internationally proven method to teach reading effectively."