Mixed up assortment of dunces (8)
I believe the answer is:
confused
'mixed up' is the definition.
('confuse' can be a synonym of 'mix up')
'assortment of dunces' is the wordplay.
'assortment' indicates an anagram.
'of'+'dunces'='ofdunces'
'ofdunces' with letters rearranged gives 'CONFUSED'.
(Other definitions for confused that I've seen before include "Bewildered, perplexed" , "Mixed up in fun codes" , "Perplexed, befuddled" , "Disorientated" , "at sea" .)