Scottish pupils were able to pass more than four out of every 10 Higher exams last year, despite getting more than half the paper wrong.
Traditionally a C pass at Higher level is awarded if pupils score more than 50%. B grades are awarded for scores between 60 and 69%, while everything above 70% receives an A.
However, each year the Scottish Qualifications Authority (SQA) adjusts “grade boundaries” to ensure pupils are not disadvantaged by papers that are too difficult or even too easy.
This year thousands of pupils signed a petition following complaints that May’s Higher maths paper was too hard.
But a Courier investigation has found that an increasing number of exams are deemed too difficult each year, resulting in pass marks being lowered to below the 50% threshold.
Over the past five years the number of exams where a pass can be obtained with less than 50% has nearly doubled.
In 2010 just 14 boundaries were shifted to below 50% but by last year that had risen to 29.
Over the same period the overall pass rate for Highers rose from 76% to 77%, peaking at 79% in 2012 and 2013.
In percentage terms, 31% of exams in 2010 could be passed with less than half the paper correct compared to 43% nearly 30 subjects last year.
Conversely, the pass mark was raised to over 50% for just one subject in 2010 and two last year.
The Scottish Conservatives’ young people spokeswoman Liz Smith said the boundary shifts may be a result of failure to prepare pupils properly for exams.
She said: “All parents, teachers and pupils want a cast-iron assurance that the SQA exams that are sat at any level are properly moderated, marked and graded according to the highest professional standards set by the marking authority.
“There is no evidence to suggest that these standards of marking have been compromised but what there has been, particularly in light of the recent complaints about the new maths Higher, is concern about the way in which pupils are being prepared for the new exams.
“It is abundantly clear that there have been issues about the availability of exemplar materials and whether course work and prelim content has fully articulated with what appeared in the exam.
“This is a matter of huge concern and it is little wonder that both the SQA and the Scottish Government are coming under intense pressure to explain why this has been allowed to happen.”
An SQA spokesman said: “At the end of every assessment period we undergo a well-established and thorough review of how the exams have performed across the country.
“Grade boundaries are the marks needed in order to achieve a particular grade for a course.
“Grade boundary meetings, which include senior SQA management and subject specialists, are part of our rigorous process to ensure high standards are maintained and involve robust discussion and decision-making.
“If an assessment is deemed to have been more or less demanding, grade boundaries may be adjusted accordingly to ensure candidates’ achievements are recognised and fair across the whole of Scotland, year on year.
“All grade boundary decisions are then published on our website with a summary of the reasons why decisions were made. Our rigorous processes are in place to ensure no candidate is disadvantaged.”