Charges that dishearten dunces (4)
I believe the answer is:
dues
'charges' is the definition.
(due is a kind of charge)
'dishearten dunces' is the wordplay.
'dishearten' means to remove the middle letters.
'dunces' with its centre removed is 'DUES'.
'that' acts as a link.
(Other definitions for dues that I've seen before include "Payments made for upkeep of church" , "Subscription to a club or society" , "Membership fees" , "subs" .)