A study 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.'...

...To test their theory, 199 students were shown one of four different versions of a fictitious student's essay which had been marked, graded and commented on by a lecturer.

Some got a high quality essay, given an A grade, complete with positive and negative comments in either red or a 'blue-green' pen.

The other volunteers got an essay that clearly was not as good and was given a C grade, again with both positive and negative comments from a teacher writing in either red or blue-green.

But for both the high and low quality essays, the volunteers were more likely to think the teacher writing in red was harsher than the one in blue - even though their grades and comments were identical.

Asked to grade the essay themselves, the students reading those marked in red would raise the good quality essay score by an average of 3.4 per cent.

Those reading essays marked in blue would raise the score of the better essay by an average 2.9 per cent.

But the gap was bigger among those given the lower grade essay to review. The students reading the one with comments in red would raise the score by 5.6 per cent.

But those reading the one with comments in blue-green ink would only raise it by 0.7 per cent,

The volunteers also associated the teachers writing in blue-green as more likely to be 'nice, enthusiastic and have a good rapport with students.'

The difference may be small but was described as 'statistically significant' by the researchers.