England’s exam regulator Ofqual says it is “closely monitoring” the marking of an A-level maths paper which students and parents say left candidates “crestfallen” because of its difficulty.

More than 20,000 people have signed a petition calling for the paper to be reviewed, claiming it was significantly more challenging than in previous years.

The founder of the petition said Wednesday’s Pearson Edexcel paper one exam left students “overwhelmed” by questions that required “multiple layers of reasoning” and “extended algebraic manipulation”.

A spokesperson for Pearson says the exam board is committed to ensuring a fair exam experience for every candidate.

The petition, published on the day of the exam, argues that grade boundaries should reflect the difficulty of the paper.

It reads: “Many candidates who had demonstrated strong mathematical ability throughout their studies found themselves unable to complete substantial sections of the paper within the allotted time.”

Students and parents have contacted BBC Your Voice to air their frustrations with the exam.

Tayub Gul, an 18-year-old student from Leeds, said that despite revising the right topics, the design of the questions caused him difficulty.

He said: “Usually if you can’t do part A of a question, you can do part B, since part A is a ‘show that’ question, [but] there were no ‘show that’ questions.

“Stuff I revised, that I knew how to do, I couldn’t demonstrate due to the design of the paper and how it was structured. I did the best I could, but it feels unfair.”

A parent from Buckingham, who did not want to be named, said their son was “crestfallen” after leaving the exam, which he was resitting after missing an A* grade – required for his preferred university choice – by two marks last year.

They said: “It’s so disheartening to see the rug pulled from under the feet of these students who have put so much effort and ability in.

“I know the grade boundaries adjust to take into account performance of the cohort, but what that doesn’t achieve is addressing the psychological effects of sitting a paper that is so different from anything you’ve seen before.”

Ofqual told PA Media that their priority is “students and ensuring their grades are a reliable indication of what they know, understand and can do”.

A spokesperson for Pearson said: “If a paper is found to be more difficult than previous years, grade boundaries will be set to reflect that.

“When setting grade boundaries, we review a range of evidence, including statistical data and expert judgment.

“This process ensures students receive results that fairly reflect their performance and are comparable across exam series.”

Additional reporting by Rozina Sini