Numeracy: Pupils struggle with sums in Wales says Estyn
Pupils in half of Wales' secondary schools and 40% of primary schools have weak numeracy skills, according to the schools watchdog.
Estyn says children struggle with basic sums, such as multiplying, and rely on a calculator. As a result, they are unable to do harder calculations.
It said schools should provide more opportunities for pupils to use their skills.
The Welsh government said the report would help to raise numeracy standards.
Ministers have long been concerned about this area. Last year, Wales lagged behind England, Scotland and Northern Ireland in the Programme for International Student Assessment (PISA), which looks at literacy and numeracy.
Estyn discovered that some pupils it saw during inspections found it difficult to carry out basic sums, such as fractions, percentages and decimals.
In a report which focused on children in key stage 2 and 3 (ages seven to 14), it also said many could not recall important number facts, such as how to multiply.
It meant young people were unable to apply reasoning to solve more advanced mathematical problems.
It pointed to a number of improvements needed, such as better monitoring of pupils and ensuring that schools have a clear numeracy policy that applies across all classes and departments.
Estyn will now track the progress of a sample of schools over the next two years, reporting on the impact of the Welsh government's new literacy and numeracy framework.
Chief inspector Ann Keane said it was key that children were taught the basic skills so they did not need to rely on calculators.
"Numeracy is still a cause for concern in schools," she said.
"We know that many schools have not given as much attention to numeracy as they have done for literacy, but it is vital that schools have clear plans for developing numeracy skills.
"The plans need to address young people's weak numeracy skills so that they can do mental arithmetic, grasp numerical reasoning and don't have to rely on a calculator.
"Basic numeracy is an essential life skill that is needed in most jobs and in managing personal finances.
"But a majority of pupils struggle to understand how numeracy is relevant to their everyday lives and this needs to be tackled."
Estyn also recommended that local authorities or education consortia should support teachers in improving their knowledge, skills and confidence in teaching numeracy skills.
Angela Burns, Conservative education spokeswoman, said the report was "worrying".
"We are competing in an increasingly global economy and if our young people cannot do simple maths, they will lose out in the jobs market to those from other countries who have the skills employers seek," she added.
Plaid Cymru said the report "confirms the party's concern about numeracy" and called for earlier intervention.
Simon Thomas, the party's education spokesperson, said: "The Welsh government cannot let this continue.
"Good teaching and improved teaching standards will be vital to the success of Wales's literacy and numeracy drive.
"Tracking children's progress throughout their education is simply not good enough - we must intervene at an early stage to give every child the best possible opportunities."
The Welsh government's approach to numeracy is "failing Wales' children", according to the Welsh Liberal Democrats.
Education spokesperson Aled Roberts added: "It is a great shame that after all this time the Welsh Labour Government is still insisting that restructuring is the best way forward to improve children's basic education.
"The real debate needs to be about standards not structures. The Welsh government needs to set out what will be done for those children who will have already lost out before any long term plans to deal with the literacy and numeracy deficit come to fruition.
The Welsh government has brought in regular reading and literacy tests for pupils aged seven to 14, which started in May.
A spokesperson said Education Minister Leighton Andrews had "made clear his commitment to improving standards of numeracy in Wales".
"This report shows where we have been successful in developing numeracy skills in our schools and in teaching numeracy across the curriculum and where performance needs to be strengthened," they said.
"The recommendations will inform the ongoing work of the Welsh government, local authorities and schools to ensure that numeracy levels are improved.
"We welcome the report's findings and congratulate those schools and local authorities highlighted whose effective approaches and collaborative work in helping to raise learners' numeracy skills are leading the way."
Answers to sample numeracy questions: Year 3: 28p; Year 4: 16 tins; Year 5: £1.05; Year 6: 90; Year 7: £34; Year 8: 256.35; Year 9: 2.76