Teachers have been told not to use red link to mark homework to avoid upsetting pupils.
The edict has been condemned as ‘absolutely political correctness gone wild’ which risks leaving students in the dark about where they have gone wrong.
Ministers have been forced to distance themselves from the bizarre policy, insisting no government rules exist on what colour pens teachers use.
The policy would appear to be at odds with the back to basics approach of Education Secretary Michael Gove who has insisted teachers must mark pupils down for poor spelling and grammar.
He has warned that in the past too little has been done to focus on core skills to ensure young people are confident in key writing skills.
Tory MP Bob Blackman revealed his anger after being told a secondary school in his Harrow East constituency had banned teachers from using red ink.
He told MailOnline: ‘A teacher contacted me and said I cannot believe I have been instructed by my head to mark children’s homework in particular colours and not to use certain colours.
‘It is all about not wanting to discourage youngsters if their work is marked wrong.
‘It sounds to me like some petty edict which is nonsense. It is absolutely political correctness gone wild.
‘My take on all this is to say children need to understand the difference between what’s right and what’s wrong.’
Tory MP Bob Blackman slammed the unnamed school in his Harrow East constituency for telling teachers not to use red ink, prompting education minister Liz Truss to insist the government has not issued a ban
Mr Blackman took his concerns to ministers, tabling a parliamentary question whether the government issues guidelines which ‘prohibit or discourage the use of red ink for the purposes of marking or commenting on students’ schoolwork’.
Elizabeth Truss, the ministers responsible for school attendance and cutting bureaucracy, insisted: ‘No, the Department does not issue guidelines which prohibit or discourage the use of red ink for marking student’s schoolwork.’
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It is thought the policy is set by the headteacher, and not Labour-run Harrow council.
Mr Blackman refused to name the school to protect the teacher who had spoken out.
But he said he was going to take the issue up with the headteacher to ensure pupils were told when they had got things wrong.
Mr Blackman added: ‘If they have got their homework wrong they need to be told it is wrong and to understand what the right answers are. The idea that they should use this or that colour is madness.’
A study by the University of Colorado warned that red is associated with 'warning, prohibition, caution, anger, embarrassment and being wrong'
Earlier this year a US study suggested that teachers should stop using red pens because the colour is associated with 'warning, prohibition, caution, anger, embarrassment and being wrong'.
Researchers showed students think they've been assessed more harshly when their work is covered in red ink compared to more neutral colours like blue.
Sociologists Richard Dukes and Heather Albanesi from the University of Colorado told the Journal of Social Science: 'The red grading pen can upset students and weaken teacher-student relations and perhaps learning.'
Chris McGovern, chairman of the Campaign for Real Education, slammed the findings saying: 'In my own experience of 35 years in teaching is that children actually prefer teachers to use red ink because they can read comments more easily.
'I think this research is misguided. The problem with using a colour like green or blue is that it's not clear. A lot of schools seem to have a culture where they don't like critcising children but actually this helps them.
'It's not intimidating children want to see where they've made a mistake. I think it's a rather silly idea.'Under the last Labour government red ink was banned in hundreds of schools because it was considered 'confrontational' and 'threatening'.