A head employed by Timbertop School (5)
I believe the answer is:
teach
'school' is the definition.
(I've seen this before)
'a head employed by timbertop' is the wordplay.
'a head' becomes 'each' (as in a phrase like '50 a head').
'employed by' is a charade indicator (letters next to each other).
'timbertop' becomes 't' (top of the word 'timber').
'each' put after 't' is 'TEACH'.
(Other definitions for teach that I've seen before include "Educate 4 across" , "Coach" , "show" , "Cheat (anag)" , "Tutor" .)