Two of England's biggest exams boards are still being too generous when awarding grades for GCSE science, Ofqual has said.
Both OCR and Edexcel were more lenient than the AQA board at grades A and C in this year's exams, a report by the exams regulator concluded.
In March Ofqual warned that standards in the new GCSE science exams had been compromised.
The quality of assessment for the qualification was a "serious cause for concern", it said.
In a damning report, looking at science GCSEs in 2007 and 2008, the regulator highlighted a number of issues which required "immediate action".
These included concerns that the exams did not challenge the brightest pupils, syllabuses were "over complicated" and there were too many "options" of papers that students could take in order to get the qualification.
In addition, Ofqual found that too much emphasis was placed on pupils sitting multiple choice, or "objective tests".
In its latest report, which looked at science GCSE exams taken this summer, the regulator noted that many pupils taking modular exams had sat many of the papers last year, when Ofqual found a drop in standards, and were "cashing in" those grades this summer. It says that although awarding bodies may have tightened standards at individual module level, the "impact on the GCSE as a whole takes time to work through".
Ofqual's analysis of predictions of grades made by each of the three exam boards against actual results showed that OCR and Edexcel appeared more generous in some areas.
An OCR spokesman said: "We welcome Ofqual's report and commentary on Science - that is what a regulator is for. The issues with Science are historic problems with the new style of specifications. We are working with the regulator to ensure that standards are aligned across the awarding bodies. We are currently half way through a two year programme and expect that by summer 2010 these differences will have been substantially reduced." Edexcel declined to comment.
