Image caption The Pisa tests - a major study of educational performance - are taken by 15-year-olds

A plan to exclude Wales from a creative thinking element in global education tests raises "serious questions", according to Plaid Cymru.

Education Minister Kirsty Williams has decided "Wales should not participate" in the creative thinking option of Pisa 2021.

Creative thinking is one of the "additional performance measures for 21st century skills", say Pisa.

Ministers have said they will provide further information by November.

The Programme for International Student Assessment (Pisa) tests - a major study of educational performance - are taken by 15-year-olds in around 80 countries every three years, as part of the work of the Organisation for Economic Co-operation and Development (OECD).

As in previous cycles, students will be tested in reading, mathematics and science, but for the first time in 2021 students can be tested in creative thinking.

A Welsh Government spokesperson said: "We will be discussing our decision with the Departments of Education in England and Northern Ireland before a decision is sent to the OECD by the November deadline.

"We will provide further information once we have written collectively to the OECD."

Plaid Cymru education spokeswoman Sian Gwenllian AM told the BBC: "This decision raises serious questions about the government's approach to the new curriculum.

"One of the aims of the new curriculum is to develop our young people into creative thinkers, so it is surprising that the education minister does not want to take this opportunity to assess that now.

"Is this a lack of capacity within the government? That in itself would be a cause for concern. Or a fear of the results? The education minister needs to explain this urgently."

A spokesman for Pisa said: "Creative thinking is the Pisa 'innovative domain' for the 2021 cycle.

"The innovative domains are the new assessments that we introduce at each cycle to get international data on important life competences in addition to reading, mathematics and science literacy.

"The innovative domains are an integral part of the Pisa assessment, but participating countries can decide to opt out and only take the main Pisa modules."

Image caption The education minister "needs to explain this urgently", says Sian Gwenllian

A Scottish Government spokesperson said it was "monitoring the development of the creative thinking option for Pisa 2021 and will take a final decision on whether to take part at a later date", while a spokesperson for the Department for Education at Westminster said: "We will confirm if we will be participating in the Pisa 2021 creative thinking assessment with OECD in line with their November deadline."

Students in Wales were the lowest of the UK nations in science, reading and maths in the 2016 tests, scoring 478 in maths, 477 in reading, and 485 in science.

After the 2016 results - the fourth time Wales had done worse than the other UK nations - the then first minister Carwyn Jones admitted that the results made for "uncomfortable reading".

A new curriculum will be introduced in Wales from nursery to Year 7 in 2022, a year later than originally planned.