Research commissioned by the Qualifications and Curriculum Authority appears to point to wide variations in the way C and D grades - the threshold to a "good" GCSE - are set by AQA, OCR and Edexcel in modern languages.
It comes almost two years after teachers raised concerns that some borderline C grade pupils were being unfairly downgraded in French and German.
Last year 440,118 pupils sat German and French. In Lancashire, more than a third of secondary schools said grades were below expectations.
This week the QCA said it had commissioned two reports analysing the standards employed by the three boards. A spokesman said it had also undertaken its own separate study into GCSE French. But the exam watchdog would not disclose the findings of the reports and said it was working towards a full review to be released before the 2006 exams.
The revelations will raise fresh concerns about the existence of more than one board, just three years after an A-level marking fiasco tested public confidence in the exam system to the limit.
Last month Paul Newton, principal assessment researcher at the QCA, called for a more "rational" approach to setting standards. In the journal, Assessment in Education, he wrote that the QCA's own code of practice, introduced after the 2002 fiasco, still left areas of uncertainty for markers.