A report, hastily published to counter Jeffrey Robinson's claims, says GCSE maths has become more demanding.
The Qualifications and Curriculum Authority report was released last week, months before its due date.
The review, the first of seven comparing GCSEs in 1995 and 1999, found higher, intermediate and foundation level papers had become more demanding because questions were harder, particularly in algebra.
There was no evidence of a decrease in student performance, according to the report.
It said: "Where the content and style of questions were similar, performance was comparable or slightly stronger in 1999."