Plaid Cymru has called for an urgent inquiry into the ongoing row over Welsh school-leavers' English GCSE results.
Party members unanimously backed a motion on the issue at the nationalists' two-day conference in Brecon.
Plaid's education spokesman Simon Thomas AM told delegates that, while he welcomed the decision to regrade pupils' papers, Wales' education minister Leighton Andrews had failed to take
responsibility for his actions.
Mr Thomas said: "He set up the system, he allowed civil servants to negotiate this with Ofqual - he allowed this situation to happen. The credibility of the exams system in Wales has been
undermined as a result."
Earlier this week, the Labour-led Welsh Government ordered the WJEC exam board to regrade English GCSE after pupils received the "injustice" of receiving lower grades than expected. At the heart of
the row is the issue of grade boundaries being adjusted for those taking their English literature and language exams between January and June.
England's exams regulator Ofqual refused to order exam boards to change any marks. But the Welsh Government has decided otherwise - prompting fierce criticism from UK Government education minister
Michael Gove who accused his counterparts in Cardiff of playing politics.
As the spat continued, which saw Ofqual and Welsh Government officials meet face-to-face, Plaid accused Wales' education minister of conducting a "mock fight" with Westminster.
Mid and West Wales AM Mr Thomas told his party's conference: "We agree with his decision to regrade the results, but he must share the blame for what happened in the first place. I don't want
Leighton Andrews to get away with it, and it's our role in the Plaid group to hold him to account."
Plaid members later passed unanimously an emergency motion which said: "The Welsh education minister needs to explain why the Welsh Government took the decision with Ofqual to require the WJEC to
change the grade boundaries in the first instance."
But Labour AM Mr Andrews appeared unfazed by the criticism - and used social networking site Twitter to say his decision had won support from one of Plaid's most senior AMs. He wrote: "Interesting!
As Plaid Cymru conference kicks off, Dafydd Elis Thomas expresses full support (to me)."