The Leaving Cert higher level maths paper has been criticised by a co-author of the New Concise Maths project maths textbooks as a disgrace.
Today's higher and ordinary level papers contained elements of the new Project Maths curriculum.
Speaking on RTÉ's Drivetime, Brendan Gildea said that 10,000 of the country's top candidates sat the paper and the majority are devastated.
"There was a question asked on the direction of causality.
"I've written the text book and I don't know the answer to that question, and really its absolutely appalling," he said.
It is also the first year that all students will be examined in part in the new Project Maths syllabus.
However, an ASTI maths spokesperson said she saw nothing fundamentally wrong with today's paper.
Maths teacher Brigid Cleary said while parts of today's exam were difficult, other parts were easy or "ok".
She said, however, that it was hard for this year's Leaving Certificate students to make the transition to the new Project Maths syllabus.
Ms Cleary said they had started secondary school learning maths in the old, traditional way and the new syllabus was challenging to students who had been encouraged previously to learn by rote.
Meanwhile, replacement papers were used in the Leaving Certificate Irish examinations after an error in distribution led to a security breach.
The State Examinations Commission prepares, prints and packs two potential exam papers for each subject and level.
The contingency is in place so that one can serve as a back-up should anything go wrong.
The Irish contingency papers replaced the Higher and Ordinary Level exams that were distributed to schools last week.
The SEC was keen to stress, however, that there was no change for students and their exam proceeded as normal.