Assured fine don works in college tutorials, principally (9)
I believe the answer is:
confident
'assured' is the definition.
(similar in meaning)
'fine don works in college tutorials principally' is the wordplay.
'works' is an anagram indicator (work can mean to twist or convulse).
'in' is an insertion indicator.
'principally' says to take the initial letters.
The initial letters of 'college tutorials' is 'ct'.
'fine'+'don'='finedon'
'finedon' with letters rearranged gives 'onfiden'.
'onfiden' inserted within 'ct' is 'CONFIDENT'.
(Other definitions for confident that I've seen before include "Trusting firmly" , "Feeling certain" , "5 [CERTAIN]" , "Bold" , "Certain, sure" .)