None in class needing correction? That’s ridiculous (11)
I believe the answer is:
nonsensical
'ridiculous' is the definition.
('nonsensical' can be a synonym of 'ridiculous')
'none in class needing correction?' is the wordplay.
'needing correction?' indicates anagramming the letters (I've seen 'needing correction' mean this (I've seen this in other clues)).
'none'+'in'+'class'='noneinclass'
'noneinclass' with letters rearranged gives 'NONSENSICAL'.
'that's' acts as a link.
(Other definitions for nonsensical that I've seen before include "Like rubbish" , "Absurd, idiotic" , "Meaningless" , "Ridiculous" , "Without meaning" .)