Last in form has flower for teacher (6)
I believe the answer is:
master
'for teacher' is the definition.
(I've seen this before)
'last in form has flower' is the wordplay.
'last in' says to take the final letters.
'has' means one lot of letters go next to another.
'flower' becomes 'aster' (type of flower).
The final letter of 'form' is 'm'.
'm'+'aster'='MASTER'
(Other definitions for master that I've seen before include "Teacher to gain control" , "With 1a [OLD], one who painted" , "Instructor" , "Skilful operator; teacher" , "One in complete control; great artist" .)