Grades have fallen in GCSE science this year despite an eleventh-hour intervention by Ofqual to save thousands of pupils from getting a U.
The Joint Council for Qualifications, which represents the exam boards, said the drop was probably driven in part by changing entry patterns following the government's shake-up of GCSE science.
As part of its exam reforms, in England the government replaced the old GCSE science, "additional science" and "further additional science" qualifications with a new double award GCSE in "combined science".
This has made it difficult to compare this year's results with last year's.
However, JCQ has come up with a comparator figure against which this year's results can be measured.
This figure comprises 16-year-old entries in science and additional science in 2017, plus early science entries by 15-year-olds in 2016.
Using this comparator, results in the double award were down this year across all the main grade thresholds.
The proportion of UK entries at A/7 and above fell 0.4 percentage points from 7.9 per cent in 2017 to 7.5 per cent this year.
Entries at C/4 and above fell by 0.6 percentage points from 55.8 per cent in 2017 to 55.1 per cent this year.
And passes at G/1 and above fell by 0.9 percentage points from 99 per cent in 2017 to 98.1 per cent this year.
Increase in entries for separate GCSE sciences
JCQ said this was probably partly explained by higher performing students opting to take separate GCSEs in biology, chemistry and physics following the government’s reforms.
In the past, many of these students would have taken science, additional science and further additional science instead.
Today's results show there was indeed a large increase in entries across the separate sciences this year.
Entries in biology increased by 23 per cent on last year, while those in chemistry rose by 18.6 per cent and physics by 17.2 per cent.
On Monday Ofqual announced that it had taken the highly unusual step of intervening over the fail grade for GCSE combined science after it found that more candidates than expected were getting an unclassified result.
The regulator allowed examiners to look at the work pupils did on the higher tier paper and judged whether it would have been enough to secure them two grade 3s, had they sat the foundation tier paper for the double GCSE.