Daughter getting behind, being less sensible (6)
I believe the answer is:
dafter
'less sensible' is the definition.
'daughter getting behind' is the wordplay.
'daughter' becomes 'd'.
'getting' says to put letters next to each other.
'behind' becomes 'after' (I've seen this in other clues).
'd'+'after'='DAFTER'
'being' is the link.
(Other definitions for dafter that I've seen before include "More foolish!" , "crazier" .)