Alma mater is traditional (3,6)
I believe the answer is:
old school
'traditional' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for old school that I've seen before include "square" , "Doing things the same way as before" , "Not influenced by newer styles" , "Those who think traditionally" , "Group favouring conservative practices" .)