Art school led by Boris, boundlessly imaginative at first (7)
I believe the answer is:
origami
'art' is the definition.
(I've seen this before)
'school led by boris boundlessly imaginative at first' is the wordplay.
'school' becomes 'gam' (both can refer to a group of whales).
'led by' is a charade indicator (letters next to each other) (some letters go in front of others).
'boris boundlessly' becomes 'ori' (I can't explain this - if you can you should give a lot more credence to this answer).
'at first' indicates taking the first letters.
The first letter of 'imaginative' is 'i'.
'gam' put after 'ori' is 'origam'.
'origam'+'i'='ORIGAMI'
Can you help me to learn more?
(Other definitions for origami that I've seen before include "Artistic paper folding" , "Artwork with paper" , "folding process" , "Creation of objects from paper" , "folding stuff?" .)