Evidence points towards a “slight bias” against boys in teacher assessments, according to England’s exam regulator.
Ofqual also said in a new report that bias against disadvantaged pupils and those with special educational needs were “common”.
The system is designed to mark students on the standard they are performing at, rather than their potential, and allows schools to use a wide range of evidence to back up judgements, including exam-style questions and homework.
On Monday, Ofqual published a literature review of studies exploring bias in teacher assessment.
The regulator said there was “no exact parallel” between the studies it looked at and grading this year, given the “unique circumstance under which teacher judgements are called upon for summer 2021”.
Its report said: “With respect to teacher assessment, evidence of teacher bias in relation to gender is mixed, but a slight bias in favour of girls (or against boys) is a common finding.”
Evidence on ethnicity and teacher assessments were “mixed”, with findings showing bias against and in favour of each minority group compared to the majority group, as well as findings suggesting no bias at all, Ofqual said.
The report added: “Evidence on disadvantage and special educational needs (SEN) is less mixed, with bias against the more disadvantaged (or in favour of the less disadvantaged) and bias against pupils with SEN (or in favour of those without) being common findings.”
It said “the greater subjectivity of teacher assessment” means this form of grading is “more vulnerable to bias than test-based assessment”.
Ofqual said it was “important for teachers to be aware of the potential risks to the validity of their judgements” and for them to “take steps to mitigate them by following Ofqual’s objectivity guidance”.
A blog from the regulator, published alongside the report, said: "Because there is more opportunity for bias to creep in to teacher-based results than test-based results, divergence of this sort is more likely to represent bias in the teacher-based results."
It added: "The literature that we drew upon was fairly limited in size and it is possible that it might have been skewed to some extent by publication bias, whereby evidence of an effect occurring is more likely to get published than evidence of no effect.
"So, it doesn’t necessarily follow that teacher-assessed grades will be biased in these ways this year."
But Kate Green, Labour’s shadow educations secretary, said the Ofqual report raised “serious concerns” about this year’s grading system.
"Teachers urgently need support from the government to ensure fair, consistent grades are awarded for all students across subjects, schools and regions but ministers are abdicating responsibility,” she said.
Earlier this year, the education select committee raised concerns over this year’s grading system, which they said could lead to a “wild west” of grades for students.
Its Tory chair warned of the potential for grade inflation and a lack of consistency between schools in a letter to the education secretary.
Ms Green added: "The Conservatives’ chaotic mishandling of exam results last summer created huge amounts of stress and pupils urgently need to know what steps will be taken to guard against inconsistent grading and ensure such disruption does not happen again."
The watchdog said teachers should mitigate the risk of bias by ensuring each judgment is based "purely upon evidence of how a student has performed" putting other factors, like attitude or behaviour, to one side.
It adds that teachers should make themselves “aware of the different kinds of unconscious cognitive biases that can compromise judgements” and think about ways to minimise them.
A Department for Education spokesperson said the Ofqual research “shows that the grading system last summer did not disadvantage students, including those from disadvantaged backgrounds”.
They added: “There is a robust guidance and quality assurance in place for this summer’s assessments, including training and support, internal checks within schools and external checks by exam boards to ensure fairness.”
Additional reporting by Press Association
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