Private schools gave out more generous GCSE grades than expected during the pandemic, new analysis suggests.

The analysis by FFT Education Datalab found that during 2020 and 2021, when full public exams were cancelled owing to the disruptions of Covid-19, private school teachers awarded higher GCSE grades than expected compared with peers working in state grammar schools.

Looking at pupils’ predicted performance in GCSE English and maths from National Pupil Database figures, FFT compared pupil performance at GCSE in selective grammar schools in the state sector with results awarded by private schools.

Prior to the pandemic, during 2017-19, pupils in both grammar and private schools tended to do better than expected based on their prior attainment at primary school – but with little difference seen between the two school types before 2020.

FFT analyst Natasha Plaister said that for the 2020 and 2021 results, when teacher-assessed grades were awarded, “pupils in independent schools exceeded their estimated grades by more than they did before the pandemic, while those in selective state schools exceeded them by less than pre-pandemic in English, and roughly the same in maths”.

She added: “This analysis does seem to suggest that during the pandemic, under both centre-assessed grades (CAGs) and teacher-assessed grades (TAGs), independent schools gave out more generous grades than might be expected.”

In 2021, private school pupils were nearly 0.7 grades higher than expected, according to the analysis, while those attending selective grammar schools achieved around 0.3 grades higher than expected.

While this could be because private school pupils were less disrupted by the pandemic, Ms Plaister said teacher-assessed grading was meant to adjust for this to some extent.

The study did have some limitations – some private school pupils do not take Key Stage 2 Sats tests, so the data would be weighted towards privately educated secondary students who attended a state primary school, and some private schools sit IGCSEs rather than GCSEs.

Ms Plaister said FFT would be looking to see if the gap between private and grammar schools started to close in the 2022 results when pupils have sat full public exams again for the first time since the pandemic.

Between 2019 and 2021, private schools boosted their share of top GCSE grades by 14.6 percentage points, with more than six in 10 pupils awarded a grade 7 or above in 2021, whereas grammar schools boosted their performance by 7.5 percentage points over the same period.