The headteacher of a trail-blazing school has warned that pupils who were affected by the controversial changes to English GCSEs grades could suffer lasting blows to their confidence.

Jo Shuter, head of Quintin Kynaston School in St John’s Wood, claims there is a danger some will lose confidence in the mantra that hard work gets results.

“Going into exams we tell all our students, it’s your responsibility, do yourself justice,” she said.

“Now when we have to say to them it wasn’t their fault, they start to lose confidence in the system and that’s hard.

“Our kids have got to have a belief that if they work as hard as they can they can succeed, go to university and change their lives. Otherwise the message we give them about meritocracy is defeated, and for working class kids that’s tough.”

The school waived the usual entry requirements for its sixth form to allow students affected by the marking changes to take up places.

They are preparing students for November re-sits offered by exam board AQA, but Ms Shuter worries this may impact on AS-level performances.

“AS-levels are challenging for all kids, but particularly for those on the C-D border line. We have to remotivate them towards a November retake, without diluting the focus on the AS course,” she said.

“These are students who deserve to have their C grade and deserve not to have to worry about it.”

Grade boundaries in GCSE English were lifted for summer exams, seeing A*-C grades in English at Qunitin Kynaston fall from 82 per cent to 68 per cent.

This is despite the department repeatedly being singled out as exceptional by OFSTED inspectors, and delivering improved results year on year.

Ms Shuter added: “I don’t have any issue with changing the rules, but you’ve got to give the schools a chance to plan for those changes.

“You can’t drop it in after the kids have taken the exam that’s totally, totally discriminatory and arbitrary.”

She is calling for exams to be remarked according to previous grade boundaries.