An investigation is under way to see if a school gave students too much help with their Highers.
The SQA has received a complaint about potential malpractice at Mearns Castle High School in East Renfrewshire.
The allegation is that candidates may have received too much assistance in Higher geography, history and modern studies projects.
Both the school and East Renfrewshire Council have strongly denied any wrongdoing.
And BBC Scotland understands there is no suggestion that candidates could get their grades changed or that work will have to be remarked.
The allegations centre on the amount of feedback offered to candidates about their projects before the final version was written up.
The assignments are worth a third of the final mark so can make a difference to a candidate's grade or even whether they pass.
A letter sent to the parents of students in February by the principal teacher of social studies at the school said candidates would be required to hand in drafts of their projects before they wrote up the final version under exam conditions.
The letter suggested students could "make the appropriate changes to their work based on feedback received from their teacher and seek additional support if necessary".
The SQA has strict guidelines about the kind of feedback candidates can be offered on projects.
East Renfrewshire Council said the letter was poorly worded but that teachers did not breach SQA rules by offering inappropriate help.
An East Renfrewshire Council spokesman said: "Our staff are well aware of the guidelines set out by the SQA in relation to Higher Assignments and these are followed rigorously across the authority. At no stage was any pupils' Higher Assignment marked.
"This letter, which unfortunately was poorly worded, was simply issued to stress the importance of these assignments to parents.
"Staff provided support and advice to pupils in preparation for completing their assignments under exam conditions, as is permitted by the SQA, which is what this letter is referring to.
"It is important to stress that the wording of this letter does not accurately reflect the role staff at this school play in supporting pupils with their Higher Assignments, and this has already been amended for the forthcoming session."
Mearns Castle, in Newton Mearns, has a relatively prosperous catchment area and a relatively high proportion of youngsters get good results in their Highers.
The school is often placed near the top of unofficial league tables produced by newspapers.
BBC Scotland understands the complaint may have been made by someone with no direct connection to the school who became aware of the letter.
An SQA spokesman said: "We have been made aware of a potential issue relating to conditions of assessment for Higher assignment work.
"SQA's criteria on assessment conditions and the assistance which teachers and lecturers can give to candidates are clearly published on our website and in course materials.
"As in all cases where potentially serious matters are raised with SQA, we will now investigate what has happened.
"SQA takes very seriously its obligation to ensure fairness and equity for all candidates in all qualifications through consistent application of assessment conditions."
'Necessary to investigate'
The SQA has published detailed guidance on how it deals with allegations of suspected malpractice.
It says: "Whether intentional or not, it is necessary to investigate and act upon any suspected instances of malpractice, to protect the integrity of the qualification and to identify any wider lessons to be learned.
"Where SQA becomes aware of concerns of possible malpractice, its approach will be fair, robust and proportionate to the nature of the concern. These procedures will be applied where SQA's view is that there is a risk to the integrity of certification, which is not being successfully managed through our regular processes."
In Scotland, exam results alone are not used as a judge of a school's performance.
It is widely accepted that, as a general rule, superficially good exam results often reflect a school's catchment area and do not provide a means of judging the quality of the teaching or the school.
However comparing the exam performance of schools with similar catchment areas is seen as productive as it can highlight possible examples of good practice or underperformance.