Contact a head teacher finally in leading position (5)
I believe the answer is:
reach
'contact a head' is the definition.
'reach' can be an answer for 'contact' (synonyms). I'm not sure about the 'a head' bit.
'teacher finally in leading position' is the wordplay.
'finally' indicates one should take the final letters.
'in leading position' becomes 'each' (I can't justify this - if you can you should give a lot more credence to this answer).
The final letter of 'teacher' is 'r'.
'r'+'each'='REACH'
Can you help me to learn more?
(Other definitions for reach that I've seen before include "Arrive at the destination" , "Get as far as" , "bay" , "Succeed in getting to" , "Get to < throw up in the old" .)