Model young pupils initially enthralled by fantastic teacher (9)
I believe the answer is:
archetype
'model' is the definition.
(I've seen this before)
'young pupils initially enthralled by fantastic teacher' is the wordplay.
'initially' suggests taking the first letters.
'enthralled by' means one lot of letters goes inside another ('enthral' can mean 'capture').
'fantastic' indicates anagramming the letters.
The initial letters of 'young pupils' is 'yp'.
'teacher' is an anagram of 'archete'.
'yp' put inside 'archete' is 'ARCHETYPE'.
(Other definitions for archetype that I've seen before include "exemplary item)" , "Original model from which others are copied" , "Original, prototype" , "Standard - cheap tyre (anag)" , "Very characteristic example" .)