Full details of the emergency arrangements for students whose exams have been cancelled have been announced.
Grades for qualifications including Highers and National 5s will be based on estimates by teachers.
The SQA has now sent full details of its plans to schools and teachers - it says it wants to ensure fairness and maintain the credibility of the system.
Exams have been cancelled this year for the first time ever.
SQA chief executive Fiona Robertson said she "fully understood" it was an uncertain time for learners as well as parents and carers.
She said: "Together with Scotland's education system, SQA remains committed to delivering results to learners, in as fair a way as possible, at this exceptionally difficult time.
"We want to ensure that young people across Scotland get the results they deserve, so they can progress to further learning or work."
Ms Robertson said the system they had produced had three broad principles:
- Fairness to learners
- Safe and secure certification which followed the latest public health advice
- Maintaining the integrity and credibility of the system and maintaining standards
The grades candidates receive will be based principally on estimates by teachers.
Teachers will have to rank candidates, say what grade they think a candidate would get and place them in a particular band for each grade. This will not simply be the result of the prelim.
Ms Robertson explained: "Teachers and lecturers are best placed to have a strong understanding of how their learners have performed and, based on their experience and the evidence available, what a learner would be expected to achieve in each course.
"An estimated grade is not just the result of one prelim or one project, but is an overall judgement based on all activity across the year."
The SQA faces a huge challenge this year.
It has to be fair to candidates in truly exceptional circumstances.
No matter how much personal sympathy there may be for learners, it cannot simply give qualifications away.
Universities want to ensure that the exam results for Highers and Advanced Highers truly reflect a candidates ability.
If all candidates passed, or if an undue proportion got As, it would risk undermining the credibility of the system and being unfair to candidates.
Nobody wants to see a good suite of results or the achievements of learners dismissed in future years as being the results from "the year exams were cancelled".
One challenge it faces is ensuring the system is fair to candidates whose work or performance may have improved since their prelims. This is one reason why estimated grades should not be based on prelims alone.
Another is to ensure there is a fair way of questioning results. This is why there will be a free appeals process this year.
The SQA will then check and validate the information it receives. It says it will moderate it, if necessary, to ensure consistency across schools and colleges and consistency with results from previous years.
It said: "We will use the information from these estimates, in addition to prior learner attainment, where this is available.
"For example, if learners achieved National 5 or Higher courses, in a previous year.
"We will also look at schools' and colleges' previous history of estimating and attainment in each subject and level.
"We may moderate these estimates, up or down, if that is required."
Education Secretary John Swinney said teachers and lecturers were "best placed" to make decisions on learners' performances.
He said: "I am confident that they can deliver this vital role to ensure learners' achievements are recognised in these unprecedented circumstances.
"I am very grateful to the Chief Examining Officer and to all at the SQA for their work in developing this comprehensive guidance."
When will results come through?
Candidates should still receive their grades by 4 August which should have been exam results day.
There will then be a free appeals process should schools feel that any candidates or group of candidates have not received the appropriate grade.
Full details of the appeals service will be sent out shortly.
However in broad terms schools would need to provide assessment evidence which would be reviewed by senior examiners