Trio, initially, or duet, badly taught (7)
I believe the answer is:
tutored
'taught' is the definition.
(tutoring is a kind of teaching)
'trio initially or duet badly' is the wordplay.
'initially' indicates taking the first letters.
'badly' is an anagram indicator.
The first letter of 'trio' is 't'.
'or'+'duet'='orduet'
'orduet' is an anagram of 'utored'.
't'+'utored'='TUTORED'
(Other definitions for tutored that I've seen before include "Rude tot (anag.)" , "Instructed" , "Privately taught" , "Gave private lessons to" , "Disciplined" .)