S-grades (standard grades) are 2-year courses that Scottish pupils take in years 3−4 (S3 and S4), when their English contemporaries are taking GCSEs. They are designed to test the whole ability range and are taken at three levels: credit, general and foundation. Intermediate 1 and 2 are designed for students who have passed S-grades at general or foundation level, and for any student wishing to take up a new subject; some schools are replacing S-grades with Intermediate 1 and 2.
Traditionally, Scottish pupils sit S-grades only in those subjects they do not propose to continue to Highers. This means that some of the ablest Scottish pupils will have only 3 or 4 subjects at S-grade.