Thousands of children are starting secondary school in the U.K. unable to read or write properly, according to school inspectors.
Education watchdog Ofsted stressed urgent action was needed to help 12-year-olds to improve their basic skills.
Ofsted said standards had risen over the past five years but one in three primary school lessons were still no better than satisfactory.
Boys in particular have shown little improvement and they fall further behind girls in test results as they grow older.
Ofsted's major study of the state of English teaching over the past five years found that pupils did not know how to improve because the quality of teachers' assessment was "consistently weak".
Miriam Rosen, Ofsted's director of education, said: "We are concerned, particularly because it will interfere with their ability to access the rest of the curriculum."
Standards in English have risen over the last five years but have yet to reach government targets.
She added: "Although it is a generally encouraging picture there are particular groups of pupils who are not benefiting."
"There is an urgent need for schools to improve the literacy skills of pupils who enter year seven (the first year of secondary school) with attainment below Level 4 (the standard expected of 11-year-olds)," Sky News quotes the Ofsted report.