Teachers at a British school are no longer allowed to use their dreaded red pens to mark students' work.

Under a new grading policy at Mounts Bay Academy in Cornwall, teachers must mark and write feedback in green, while students must reply in purple.

"Students make more progress if it is a dialogue and the new system is designed to help that," Headteacher Sara Davey told the Cornishman newspaper.

"A lot of primary schools are already using a similar system amazingly well and I think it was felt that red ink was a very negative colour."

The Campaign for Real Education, which says it fights for "higher standards and more parental choice in state education," has taken a stand against the policy.

"The problem with using a colour like green or blue is that it's not clear," chair Chris McGovern said.

"A lot of schools seem to have a culture where they don't like criticizing children but actually (red ink) helps them."