Candidates sitting a courses at Intermediate 1, Intermediate 2, Higher and Advanced Higher levels were required to have passed a NAB for each unit in order to sit the end of course examination.
A pass in the NAB is required for the pupil to continue with the rest of the course and to sit the final exam.
Each pupil is allowed a resit if they fail their first NAB, but if they fail the resit their individual situation will be considered by their teacher, who will then decide whether they are allowed to continue with the rest of the course.
However, the time allowed for each NAB often varies depending on the specific subject.
The NABs are often made up of "core" course (grade "C") type questions, allowing candidates of all abilities to gain a pass.