Flowers provided by teachers when head is absent (6)
I believe the answer is:
asters
'flowers' is the definition.
(aster is a type of flower)
'when head is absent' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'head is absent' becomes 'ters' (I can't justify this - if you can you should believe this answer much more).
'as'+'ters'='ASTERS'
'provided by teachers' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for asters that I've seen before include "Stares oddly at the flowers" , "Stares at bright flowers" , "Stares around at the flowers" , "A rest's a change from flowers" , "Christmas daisies" .)