Pupils who sat GCSEs this year were so nervous about their exams that they suffered from anxiety, panic attacks and insomnia, according to headteachers.
The heads also said they had never seen a year group face so much uncertainty over grades and progression to sixth-form.
GCSE grades due out on Thursday are expected to be at a rough midpoint between those of 2019 and 2021 to represent a return to normality while reflecting the challenges of the pandemic.
Heads who spoke to the Guardian worried that students from disadvantaged backgrounds who missed out on more learning would be disproportionately affected by grade deflation.
