School with old-fashioned exterior is blown up (9)
I believe the answer is:
detonated
'is blown up' is the definition.
(I've seen this before)
'school with old-fashioned exterior' is the wordplay.
'school with' becomes 'eton' (famous UK public school. I am not sure about the 'with' bit.).
'old fashioned' becomes 'dated' (I've seen this before).
'exterior' is an insertion indicator (some letters go on the outside of others).
'eton' inserted into 'dated' is 'DETONATED'.
Can you help me to learn more?
(Other definitions for detonated that I've seen before include "let off" , "Blown up" , "Set off" .)