Leaving Cert students opting to do a written exam won't know what their calculated grade would be before sitting the paper.
But they'll be given the higher of the two scores when it comes to working out their CAO points.
A timetable for the exams will be published today.
Education Minister Norma Foley says students will be presented with a choice.
However the ASTI says it is bitterly disappointed the predictive grading only model won't take account of coursework or projects completed.
President of the teachers union, Ann Piggott, says there are issues with the process
