Inspectors are set to get tough on schools with low literacy levels as part of a reorganisation of the inspection system, TES Cymru can reveal.
Estyn has decided to make literacy a priority in its new framework, to be introduced in September, after reviewing evidence from the pilot inspections and the chief inspector's annual report.
The focus will be on literacy levels on every inspection, particularly in secondaries. Inspectors will look closely at reading and writing schemes and support for struggling pupils.
In her first interview since taking over the job, Ann Keane, Estyn interim chief inspector, told TES Cymru that improving literacy is an "absolute necessity".
"We need to make sure that more pupils are up to their chronological age in terms of reading and writing so they can benefit from the whole range of the curriculum," she said.
"Inspectors will be looking at the written materials across the curriculum and their appropriateness for pupils; how materials are differentiated for different pupils; and how schools support pupils, not just those with special needs but the ones operating at an average level.
"A lot of pupils can hide low literacy levels, and they are the ones that end up not functionally literate."
Statistics show that literacy falls suddenly between the ages of 11 and 14. According to Assembly figures, almost 30 per cent of 14-year-olds failed to achieve the expected levels in reading and writing last year, compared to just 19 per cent of 11-year-olds.
Ms Keane said that many schools are working hard to improve literacy, and that inspectors will highlight examples of best practice.
"The better schools are the ones that have done the most work to develop literacy across the curriculum," she said. "We want to reflect what's going on in the best schools, and we want others to learn from that."
David Egan, professor of education at the University of Wales Institute, Cardiff, welcomed Estyn's new focus. "I think it's very sensible," he said. "We have got a huge problem with levels of literacy.
"Perhaps what Estyn is recognising is that we have now got to up our game. We are realising that this laissez faire attitude that we leave local authorities and schools to come up with the right approaches is no longer good enough."
Estyn has recently released guidance documents for teachers aimed to improve literacy, especially among boys. It said teachers need a better understanding of boys' characteristics and behaviour to bring out the best in them.
Dr Heledd Hayes, NUT Cymru's education officer, said teachers would welcome Estyn's move. "Literacy is vitally important," she said. "Obviously it's still early days and we would want to see exactly how it is inspected, but it is right that it's seen in a cross-curricular context."