Estyn's maths report criticises 'disappointing' results
"Disappointing" standards in maths among 14 to 16-year-olds in Wales must be tackled, says an education watchdog.
Estyn's report said maths was the lowest performing core subject at key stage four - when pupils work towards GCSEs - and the lowest in the UK.
Last year the proportion of students in Wales achieving C grade and above at GCSE lagged well behind England.
The Welsh government said the report had highlighted both successes and areas that could be improved.
Estyn said schools must work hard to raise standards.
Chief inspector Ann Keane said some employers were having to invest in numeracy skills training for school and college leavers.
"Many Welsh employers are concerned at the lack of mathematical skills demonstrated by employees," she said.
The Estyn report by inspectors said there was a lack of support for the professional development of mathematics teachers.
The findings and recommendations were drawn from visits to 18 secondary schools around Wales.
The report recommended more support, advice and professional development opportunities should be provided for schools.
It highlighted best practice at some schools such as Bishop Gore Comprehensive School in Swansea where it said 20% of pupils gained A* or A grades in GCSE maths in 2012.
But the report found there was an 11 percentage point gap between England and Wales in the number of students getting a C grade and above last year.
Its author Rob Davies told BBC Radio Wales: "Inspectors are noting that schools are setting their sights too low and and focusing too much on just doing enough to reach grade C and not stretching pupils enough."
He pointed to various factors affecting results in Wales.
"I think there are question marks over whether key stage three [age 11-14] is preparing pupils suitably in Wales," he said.
"The inspectors have noted that pupils lack confidence in key aspects such as number work and algebra skills.
"They are the foundations of mathematics and they give pupils the skills to solve problems."
Mr Davies said the weaker results were a combination of low expectations, poor teaching in some cases and the current set up of the GCSE, which allows schools not to enter pupils for higher grade material which Mr Davies said too many schools in Wales were doing.
He also said too many weaker students were being entered early for the exam, and that there needed to be more consistency across Wales about networking between schools and sharing good practice.
Last year the Federation of Small Businesses (FSB) published a survey saying there was a "disconnect" between what employers needed and the basic skills of young job seekers.
In July, the Welsh government revealed plans to introduce at least four new GCSE exams from September 2015, including two in numeracy and mathematics.
It followed a qualifications review in Wales for pupils aged between 14 and 19 also affecting English language and Welsh exams.
A Welsh government spokesperson said: "This report shows where we have been successful in developing mathematics in our schools at key stage four, and where we need to sharpen our performance.
"We welcome its findings and want to congratulate the schools highlighted in the report for their diligence and commitment to improving standards.
"We have clear evidence that, at an operational level, the best results in mathematics teaching at key stage four are achieved where schools and regional consortia work together, and where teachers have opportunities to share best practice and benefit from appropriate professional development and regular network opportunities."