Literacy warning from Estyn school inspectors in Wales
School inspectors have expressed fresh concern at literacy standards among 11 to 14-year-old pupils in Wales.
A report by Estyn found the standard of reading and writing at key stage 3 much lower than children's verbal skills.
Inspectors also warned that pupils with communication qualifications were not always applying their skills in class.
The Welsh government has welcomed the report and said its recently published National Literacy Programme set out a plan of action to improve matters.
The Estyn report - Literacy in key stage 3 - is based on inspectors' visits to a sample of 21 secondary schools and completed questionnaires from more than 50 secondary schools.
It also looked at inspection evidence from secondary reports and key stage 3 data from 2009 to 2011.
While girls performed better than boys, standards in English were lower than for other core subjects, although standards for Welsh as a first language were much higher.
Estyn noted that more secondary schools were giving pupils opportunities to gain Essential Skills Wales communication qualifications.
But inspectors found that children were not necessarily applying such skills consistently across the curriculum, and only a minority of schools surveyed were carrying out audits of pupils' literacy skills.
Chief inspector Ann Keane said eradicating poor standards of literacy was one of the main challenges facing education in Wales.
"Too many pupils have a weak grasp of literacy skills which affects how well they do at school," she said.
"Even when pupils do well in external assessments of their Welsh or English, their literacy skills are not always strong enough for them to apply these skills fully and confidently in other subject areas."
Mrs Keane praised the emphasis many schools were placing on key skills, including the appointment of literacy co-ordinators, but said it was too early to judge their impact.
The report makes a range of recommendations for schools, local authorities and the Welsh government, from tracking and monitoring the impact of literacy strategies to providing better guidance and support for teachers.
The report's author Jackie Gapper added that literacy was the "top priority" for those schools surveyed.
She told BBC Wales: "Although standards in English or Welsh first language have shown a steady improvement, we know that pupils applying their literacy skills across the curriculum is still a concern.
"The way pupils speak and listen in classes and to each other is more confident and assured than their reading and writing skills.
"One of the recommendations we make in this report is that there should be more guidance and support for schools to help pupils make sure they are improving those opportunities to apply the skills.
"Although they might be achieving in English or Welsh in their subject areas, they're not applying their skills across the curriculum as well as they could be."
But Ms Gapper added: "Until we have a national reading test, it's difficult to measure pupils' reading ability and progress across schools because different authorities and schools are using different tests and measuring those differently."
The Welsh government said it welcomed the report which would inform its work on improving literacy.
"Poor literacy skills affect not just the achievements of learners in Welsh or English but also their ability to make good progress in other areas of the curriculum," said a spokesperson.
"We have made clear our commitment to improving literacy standards in our schools. The recently published National Literacy Programme sets out the actions we will take to achieve this."
But Angela Burns AM, the Conservatives' education spokeswoman said the report provided "further cause for concern" about literacy failings in schools.
"It appears to validate Estyn's previous evidence that as many as 40% of young people start secondary school unable to read properly," she said.
"If a child is struggling with basic literacy skills, it will set back both their confidence and performance in almost every other subject.
"We still need reassurances from the education minister that his latest attempt to raise literacy standards will attract the support of teachers, parents and school governors and will be effectively monitored."
Published in May as a consultation document, the National Literacy Programme is the Welsh government's five-year plan to set national standards in reading and writing for teachers and pupils to work towards.
It includes national reading tests for five to 14-year-olds due to be introduced in May 2013.
The programme's ambition is for Wales to be among the top 20 nations in the Programme for International Student Assessment (Pisa) by 2015, after the 2010 Pisa rankings provoked an outcry.
Wales was the lowest ranked UK nation for reading at joint 38th of 67 nations, also lagging behind former Communist states such as Latvia and the Czech Republic.
Business organisation the Confederation of British Industry (CBI) has also pointed to the Pisa rankings as showing the need for urgent action to improve children's literacy.