CONCERNS have been raised about what are said to be surprisingly low marks for GCSE English language exams which were sat earlier this year.
The grades have been questioned by the Association of School and College Leaders (ASCL).
In 2012 thousands of GCSE English exam papers were regraded because of concerns they had been marked down.
ASCL Cymru secretary Robin Hughes said: "A few heads contacted us as soon as they received the results because they were shocked at how unexpectedly low they seemed to be."
He said ASCL then did its own research calling other schools.
"Almost all are saying that there's something odd going on," Mr Hughes said.
"We have now contacted all members and asked them to get in touch with feedback. These results are too important to schools, to teachers and, most of all, to pupils for there to be any doubt about them."
The results are for units in the first GCSE English language course to be made specifically for use in Wales only.
A spokesman for the Welsh Government said it was misleading to try to make direct comparisons between units.
"Also, the entry for January 2014 was much higher than for January 2013, with schools deciding to enter a greater proportion of learners before the end of the course.
"What is important is the overall outcome when learners cash-in their GCSE English Language results in the summer."
There was more emphasis on spelling and grammar in the exams because more people took them, according to Gareth Pierce, the WJEC's chief executive.
He said students also had to analyse an unseen piece of literary text in the exam, whereas in 2013 they were tested on a piece of writing they had studied, and in a controlled assessment, not an exam environment.
"Those teachers with concerns regarding specific candidate results have access to our enquiries about results service on our secure website where they can request clerical re-checks and access original exam papers," he said.