Why adults can't read can be traced back to a lack of formal pre-school education.
Pupils who are likely to be illiterate or innumerate as adults can be spotted as soon as they start school.
John Bynner, of the Institute of Education in London, has tracked the lives of 17,196 people since their birth in 1970. His latest research examines the obstacles faced by those in the study with poor literacy and numeracy skills.
He found signs of future difficulty could be seen at a very early age. "Cohort members with the poorest grasp of literacy or numeracy were less likely to have had formal pre-school educational experiences," he said.
By the age of 5, many were already behind their classmates in language development and visual and motor co-ordination skills. By the end of the primary school years, many had fallen even further behind in English and maths.
But schools often failed to identify these struggling pupils. Only half of the adults with poor skills said their difficulties had been recognised when they were children. "The needs of half of them remained invisible," Professor Bynner said.
Only a third of those adults with literacy difficulties received additional help from their schools when they were 10 years old.
By the age of 16, adults with literacy problems often claimed to dislike school. They were likely to leave full-time education at the earliest possible opportunity, often with no qualifications.
Many believed that on-the-job work experience was more important than academic qualifications, and that post-16 education simply delayed unemployment.
Professor Bynner found that there was rarely any difference in the quality of teaching received by literate and illiterate adults. Instead, many of them shared common elements in their home lives. For example, as children they often lived in rented or shared accommodation.
Almost a third of adults with the lowest levels of literacy lived with five or more people when they were 5 years old. Their parents were likely to have few or no qualifications and to have reading difficulties themselves.
As adults, these failing children tended to experience regular periods of unemployment. Men were more likely than their peers to be still living with their parents at the age of 34. Women were more likely to have become mothers at a young age.
Professor Bynner concluded that many pupils were set on a "trajectory of disadvantage" at a very early age. He said: "Education is the critical means of bringing about the shift that is needed, not only for economic reasons, but to ensure that people whose lives are at times hampered by accumulated difficulty can move on to a more positive path.
"Much more needs to be done."
Basic skills: the fundamentals
- Run family literacy and numeracy schemes from school, working with grandparents as well as parents.
- Encourage families to use libraries.
- Ensure teachers or teaching assistants make time for one-to-one reading with every child so that problems can be quickly spotted.
- Embrace a mix of literacy methods, and be flexible enough to use a range of approaches to meet the needs of different children.
- Accept that some methods will not work for certain children.
- Ensure a flexible curriculum, with pupils given a range of books, stories and writing exercises. This helps to increase familiarity with words.
- Work together with pre-school and further education staff to learn from one another's approaches.
Source: Ursula Howard, director of the National Research and Development Centre for Adult Literacy and Numeracy.