More work is needed to toughen up the qualification and rectify inconsistent standards between exam boards, according to Isabel Nisbet, chief executive of Ofqual.
In an interview with the Times Educational Supplement she said that there had been a “collective falling short of the standards that young people and teachers have a right to expect”.
In March last year, Ofqual published a highly-critical assessment of the qualifications taken by students in 2007 and 2008.
The exams failed to challenge the brightest pupils and contained too many multiple choice papers, it said.
And last month, a report looking at last year’s entries, found there was still “evidence that standards are currently too low”. In one case, students only needed six marks to score a C on a paper, it found.
About 802,000 pupils sat GCSEs in science and additional science this year.
Ms Nisbet said the problems with the qualifications were the fault of awarding bodies, regulators and ministers, and the development of the exams being rushed.
She added: “What (pupils and teachers) should know is that their exams have been fairly and consistently marked, rigorously checked, and therefore if they get a C or a B or an A, this is a real achievement.
“They should not feel devalued by what has been a perfectly legitimate, finely-tuned criticism at a level of sophistication which many countries would just not recognise.”
Yesterday, figures showed tens of thousands of seven-year-olds were still struggling with basic maths and literacy. Nearly one in five seven-year-olds, around 104,700 pupils, are failing to reach the standard expected in writing.
GCSE results: Page 10.