School's first head taking notice in misery (7)
I believe the answer is:
sadness
'misery' is the definition.
(both can mean unhappiness)
'school's first head taking notice' is the wordplay.
'school's first' becomes 's' (1st letter of 'school').
'head' becomes 'ness' (ness is a headland).
'taking' indicates putting letters inside.
'notice' becomes 'ad' (both can mean an advertisement).
's'+'ness'='sness'
'sness' placed around 'ad' is 'SADNESS'.
'in' acts as a link.
(Other definitions for sadness that I've seen before include "blues" , "Misery" , "regret" , "no joy there" , "Sorrowfulness" .)