The statistic is contained in new research published as part of Library Power, this week's campaign, co-sponsored by The TES, to highlight the importance of books in children's lives.
Ross Shimmon, chief executive of the Library Association which conducted the research, called the findings "shocking". He said: "The Government needs to recognise that libraries are not an optional extra in the education process. "
The LA issued a call for schools and education authorities to have statutory responsibility for standards in school libraries.
The manifesto says the Department for Education should collect statistics on libraries, formulate minimum standards to be monitored by the Office for Standards in Education, and encourage schools to employ professional librarians.
The association has also published a rating system and checklist for parents and teachers to judge how well children are served by their school and local libraries.
The survey, the first to be conducted since a Government study in 1979, looked at the combination of school and public libraries available to children in 100 postcode areas earlier this year. It showed that:
* the average expenditure on books and other resources per pupil per year in secondary schools is Pounds 4.18, while the average price of a book is Pounds 9.82. The Book Trust recommends that school libraries should spend at least Pounds 15.11 for each secondary child and Pounds 11.13 for primary pupils on books alone;
* overall expenditure on school libraries is expected to drop by 5 per cent in secondary and 8.6 in primary schools in this financial year;
* more than half of primary and middle school libraries open for less than 31 hours a week;
Details of the checklists and the research available from the Library Association, 7 Ridgmount Street, London WC1E 7AE.