Where pupils learn about morals - so unusual before start of school (10)
I believe the answer is:
classrooms
'where pupils learn' is the definition.
'about morals so unusual before start of school' is the wordplay.
'about' becomes 'c' (abbreviation for 'circa'**).
'unusual' is an anagram indicator.
'before' says to put letters next to each other.
'start of' indicates taking the first letters.
The initial letter of 'school' is 's'.
'morals'+'so'='moralsso'
'moralsso' with letters rearranged gives 'lassroom'.
'c'+'lassroom'+'s'='CLASSROOMS'
(Other definitions for classrooms that I've seen before include "Places for lessons" , "instruction areas" .)