Welsh pupils' literacy lagged behind England in 2007
Children aged seven in Wales were lagging behind their contemporaries in England in 2007 when it came to literacy, a detailed study has found.
Research shows that while pupils in the two countries scored equally for numeracy, the gap in literacy levels increased as they grew up.
Prof Chris Taylor of Cardiff University said Welsh seven-year-olds were a month behind in vocabulary in 2007.
The Welsh government said measures to improve literacy had been introduced.
The Centre for Longitudinal Studies, which looks into child development, has been following the educational achievements of 19,000 babies born in the UK in the year 2000-2001, with 2,000 of those coming from Wales.
When they were tested aged three, children in Wales were on a par with England in terms of their literacy standards, although Scottish youngsters were ahead of them.
In the subsequent years, English pupils have jumped ahead of the rest of the UK in terms of their literacy achievements, with Wales lagging behind.
Prof Taylor, who has analysed the data, said that although Welsh children being a month behind in their vocabulary did not seem that much, there were fears the decline in standards would continue.
"The interesting thing will be when these children are next tested when they are aged 10 to 11 at the start of next year," he said.
He said the figures had to be treated with caution as the tests for seven-year-olds were carried out in 2007, although the data had only recently been made available.
Since then there have been a lot changes in Welsh education such as the introduction of the foundation phase for children aged three to seven.
It started in 2008, encouraging the youngest pupils to use their imagination and learn through play and outdoor activities.
There is also the Welsh government's Literacy and Numeracy Framework (LNF), aimed at improving standards.
"If the gap continues to grow between England and Wales at the next tests, it might be felt that these reforms have not made much difference," said Prof Taylor.
"On the other hand we may find the gap has closed. But at what price?
"Currently the figures show that England scores badly in terms of the projected wellbeing of children - pupils in Wales and Scotland enjoy school more.
"Will higher academic achievement be the trade off for that enjoyable school experience as they experience more pressure?"
Prof Taylor's research takes into account data on the children's backgrounds and development to ensure the UK comparison is fair and reliable.
"Interestingly, it doesn't seem to matter if you're rich or poor - the richer children in Wales are still performing worse than richer children in England," he added.
Prof Taylor said initiatives in London focusing on literacy could be making a difference there.
The Welsh government said it had been "absolutely clear that standards and performance in Wales, particularly in literacy and numeracy, need to improve".
It said it had already introduced measures to make this happen, including the LNF, which has become statutory in schools from this month, and national reading and numeracy tests.
"In May, for the first time, pupils across Wales took our new national reading and numeracy tests," said a spokesperson.
"The results of the tests give us a much better idea about how Welsh learners are performing in relation to their peers.
"We will use the results as the basis for discussions with local authorities... about what actions can be taken to iron out variations and improve reading and numeracy performance across the board."