GCSE students have been warned to expect disappointing science grades this week as a "toughened-up" syllabus and strict marking guidelines take their toll.
Hundreds of thousands of teenagers will receive their GCSE grades on Thursday, helping determine their future prospects.
But pupils who took one of the combined science papers may miss out on hoped-for marks, after Ofqual, the exams regulator, told exam boards that this year's students must perform at higher standards than their 2011 predecessors to achieve the same grades.
This is because a new syllabus for the exam has been devised to make it tougher following Ofqual's concerns that the previous syllabuses "didn't adequately test the subject content and weren't sufficiently demanding".
All the science syllabuses were changed as a result, but only the new syllabus for the broader science paper is being marked this year. Those in the separate sciences – biology, chemistry and physics – do not kick in until summer 2013.
In its policy document drawn up for this year's GCSEs, Ofqual says GCSE science is exempt from its controversial "comparable outcomes" policy – whereby grades and pass rates should be roughly in line with the previous year.
Ofqual has always stressed that high-achieving candidates will still get the grades they deserve under the new policy and exam boards say they are not doing anything differently following Ofqual's intervention.
The GCSE results warning comes after it was revealed last week that the percentage of A and A* grade passes at A-level went down by 0.4 per cent this year – the biggest drop in the 50-year history of giving grades in the exam.
The impact of the science marks – coupled with the general exhortation to peg grades and pass rates at a similar level to last year – is likely to mean any rise in the GCSE pass rate will be limited this year.
The percentage of candidates getting A* to C grade passes has risen every year since 1988 – when students first sat the exam – from 42.5 per cent to 69.8 per cent last year.
Efforts have been made to improve the performance of boys in the past couple of years. At present they lag behind girls – 73.5 per cent of whom obtain five A* to C grade passes – at all levels. This could mean there will still be a slight rise in the five A* to C grade pass rate.
Where the difficulty comes in is over the new league table measure of five A* to C grade passes including maths and English – which has seen a substantial rise since first being introduced by Labour in 2006.
The Education Secretary, Michael Gove, has set new, minimum targets for schools, saying 40 per cent of pupils should achieve this by next year and 50 per cent by the next election in 2015. At present, the target is 35 per cent.
Headteachers' leaders predict that – if the exam boards follow the "comparable outcomes" policy – fewer schools will be able to reach those targets and more heads will face the sack and have their schools forced into becoming academies as a result.
"I can imagine that headteachers are pretty upset about Ofqual's new rigour," said Professor Alan Smithers, head of Buckingham University's Centre for Education and Employment Research.