Old school mother found in change (4,5)
I believe the answer is:
alma mater
'old school' is the definition.
(I've seen this before)
'mother found in change' is the wordplay.
'mother' becomes 'mama' (mama informally means mother).
'found in' means one lot of letters goes inside another.
'change' becomes 'alter' (altering is a kind of changing).
'mama' put into 'alter' is 'ALMA MATER'.
(Other definitions for alma mater that I've seen before include "College from which one has graduated" , "Former college" , "Alert mama to the old school" , "One's place of education" , "One's old university" .)