One's enthralled by subject in school essay that shows creativity (8)
I believe the answer is:
artistry
'creativity' is the definition.
(I've seen this before)
'one's enthralled by subject in school essay' is the wordplay.
'one's' becomes 'is' (Roman numeral).
'enthralled by' means one lot of letters goes inside another ('enthral' can mean 'capture').
'subject in school' becomes 'art' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'essay' becomes 'try' ('try' can be a synonym of 'essay').
'art'+'try'='arttry'
'is' inserted into 'arttry' is 'ARTISTRY'.
'that shows' is the link.
Can you help me to learn more?
(Other definitions for artistry that I've seen before include "great skill" , "Skilled workmanship" , "Virtuosity - craftsmanship" , "poetic skill" , "Finesse" .)