The Guild Approved Status (also known as G.A.S.) is a status on which all witch academies (or wizard academies) must have in order to teach and stay running.

The status is probably given out by The Witches' Guild.

G.A.S. Academies

Academy Headteachers
Miss Cackle's Academy for Witches
Camelot College
Pentangle's Academy for Witches