Polish maybe experiencing popularity, adopted by school (6)
I believe the answer is:
finish
'polish' is the definition.
(as in polishing or finishing a surface)
'experiencing popularity adopted by school' is the wordplay.
'experiencing popularity' becomes 'ni' (I am not sure about this - if you are sure you should believe this answer much more).
'adopted by' means one lot of letters goes inside another (I've seen this in other clues).
'school' becomes 'fish' (group of fishes).
'ni' going within 'fish' is 'FINISH'.
'maybe' is the link.
Can you help me to learn more?
(Other definitions for finish that I've seen before include "Refinement in social graces" , "Conclude, wind up" , "Perfect" , "Deal with" , "Bring to an end" .)