No school should be lacking shape (8)
I believe the answer is:
formless
'lacking shape' is the definition.
(I've seen this before)
'no school' is the wordplay.
I cannot quite understand how this works, but
'no' could be 'o' (resembles 0 - 'no' can mean 'zero') and 'o' is found in the answer.
'school' could be 's' and 's' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'should be' is the link.
Can you help me to learn more?
(Other definitions for formless that I've seen before include "Lacking shape" , "Blobby" , "Without shape" .)