Poke a drop-out (4)
I believe the answer is:
prod
'poke' is the definition.
(I know that poke can be written as prod)
'a drop-out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'drop' with letters rearranged gives 'PROD'.
(Other definitions for prod that I've seen before include "Poke - remind" , "Induce action (with stick etc?)" , "Poke with a stick" , "Stimulus" , "Spur or goad" .)