Attending only some? Never! (3,2,3)
I believe the answer is:
not at all
'never' is the definition.
(thesaurus)
'attending only some?' is the wordplay.
I cannot really see how this works, but
'attending' could be 'at' (I've seen this in other clues) and 'at' is found within the answer.
'some?' could be 'a' and 'a' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for not at all that I've seen before include "By no means - polite disclaimer" , "You're welcome" , "acceptance of apology" , "Don't mention it!" , "My pleasure" .)