The head of the government's education watchdog called yesterday for action to improve the standards of reading in England's primary schools, warning that the gap between children who could read and those who could not was widening.

Ofsted's chief inspector, David Bell, criticised "lacklustre" teaching in the worst-performing schools, claiming teachers were often too ready to blame low attainment on children's background or poor parental involvement.

The knock-on effect was that children were turning their backs on reading for pleasure, a situation exacerbated by growing home use of the computer and schools' failure to encourage pupils to use their library facilities, Mr Bell said.

The new report from the Office for Standards in Educa tion, Reading for Purpose and Pleasure - An Evaluation of Reading in Primary Schools, showed that continued improvement in reading standards was being marred by an increasing gulf between those schools that successfully tackle weaknesses in reading and those that do not.

The Department for Education and Skills has released figures showing that in 2,235 primary schools (roughly 10%), a third of 11-year-olds do not reach the standard expected for their age, down on more than 6,100 in 1997. But Mr Bell said he remained worried about this group of schools which were failing to make any progress.

"Today's findings are unacceptable," he said. "Although standards in reading are rising, we have yet to ensure that all our pupils are competent and confident readers by the time they leave primary school. A stubborn core of pupils at the bottom of the scale are being let down by the system."

The most effective teaching included the systematic daily teaching of phonics, while formal "reading records" were found to be one of the weakest aspects of teaching reading, the report found.

The shadow education secretary, Tim Collins, said: "For a government that promised so much for education in general and literacy in particular, this report makes for dismal reading. When will ministers realise that the arbitrary setting of targets for reading and writing is just not the answer?"

But the schools minister, Stephen Twigg, said: "It is vital that every child receives the best support possible in learning to read. We know that there is a tail of underachievement. We will continue to build on the success of the primary national strategy to address the concerns Ofsted raises to ensure schools have the necessary support to improve further."

· Primary school children in England have improved their performance in science and maths, although pupils at secondary school are still lagging behind many of the country's international rivals, according to a study published yesterday.

The survey, which tested 360,000 students in more than 40 countries, showed that 10-year-olds had made significant improvements in both subjects and are now ranked fifth in science and 10th in maths.

But by the age of 14, Year 9 pupils had slipped to sixth in science and 18th in maths.