Accredited Grades will be generated for all of this year's Leaving Certificate students, even in subjects where they have not opted to receive them.
The move is part of contingency planning to prepare for possible disruption to the June exams due to Covid outbreaks or other factors.
In guidelines issued to schools on Thursday, teachers have been instructed to prepare estimated marks for all students, in all subjects, regardless of the choices the student may have made.
The State Examinations Commission has confirmed that it is a precautionary measure to cover circumstances where it becomes impossible to run the examinations in one or more centres because of a Covid outbreak, or where a student or a number of students are unable to sit one or more exams due to illness or a requirement to isolate or restrict their movements, or as a result of a bereavement.
The SEC says it is also necessary to generate Accredited Grades for all students so that more accurate national standardisation can be achieved.
However, it says that while Accredited Grades are being created for all students in all subjects, in the normal course of events they will only be awarded to students who have opted to receive them.
The vast majority of students who have registered for this year's assessment options - more than 90% - have chosen to sit examinations and receive Accredited Grades in one or more subjects. The SEC has yet to collate a more detailed breakdown of the combinations students have registered.
Students have until 6pm today to confirm their choices.
According to the guidelines issued to schools this week, the process of creating estimated marks for students will begin in schools on Friday 14 May.
Teachers have been given two weeks from that date to review records of students' work and other available information, with a view to arriving at an estimated mark for each student.
Teachers have again been reminded that estimated marks should be based on their professional judgement, "suitably informed by relevant data, but not overly constrained or dominated" by that information.
The SEC has again advised schools against using data from mock exams. The guidelines state that mock exams "are neither required nor recommended for use as evidence for the Accredited Grades process".
Between Monday 31 May and Thursday 3 June, schools must complete a wider process of aligning all subject marks across the school, and they must transmit the marks to the State Examinations Commission.
The marks submitted by schools will then be subjected to a national standardisation process carried out by the SEC.
Students have until 6pm today to confirm their choices on the SEC's student self-service portal.
Despite the fact that they already registered their choices in March, all of this year's Leaving Certificate candidates are required to again confirm whether they wish to sit the exams or receive Accredited Grades or both, and to finalise the level at which they wish to be awarded Accredited Grades.
The SEC extended the deadline to this evening when it emerged late yesterday that around 10% of students had yet to complete this necessary step.