Headteachers said Norfolk students affected by last summer's English GCSE fiasco would struggle to understand a court ruling yesterday which dismissed a legal challenge by pupils, schools and unions at the same time as admitting learners had been treated unfairly.

A High Court judge agreed that students assessed in June 2012 'were to some extent subject to tougher assessments than their January counterparts'.

But Lord Justice Elias, who was sitting with Mrs Justice Sharp, said exam boards and regulator Ofqual had not acted illegally.

Dismissing a bid for a judicial review, the judge said: 'I am satisfied that it was indeed the structure of the qualification itself which is the source of such unfairness as has been demonstrated in this case and not any unlawful action by either Ofqual or the AOs [exam boards].'

Last night Norfolk headteachers said the ruling was a 'bitter blow' for the many students affected.

Jon Platten, principal at the Open Academy, in Norwich, said: 'Unfair but not illegal is quite a difficult message for the young people who have been affected by this. It will affect them for a very long time – if not for the rest of their lives.'

The legal action had been brought by an alliance of pupils, schools, local councils and teaching unions from across the UK following the publication of GCSE results last August when many students found they had missed out on an all-important C-grade in English.

Exam boards later admitted they had moved grade boundaries on a controlled assessment between January and June. But yesterday's court ruling decided Ofqual had acted in order to maintain 'the currency of the qualification' which Lord Justice Elias decided was 'legitimate justification' for the unfairness.

Notre Dame High School in Norwich saw its results significantly affected by the grade boundary change.

Headteacher Brian Conway, who was disappointed with the ruling, said the experience had made him nervous about the exams this year and was putting students in for English in January and June to allow for retakes.

'I feel we were forced into that. I feel we have to give our students the best chance,' he said.