Maybe reading old Norse work about serpent (5)
I believe the answer is:
adder
'serpent' is the definition.
(type of snake)
'maybe reading old norse work about' is the wordplay.
'maybe reading' becomes 'R' (one of the three R's of education).
'old norse work' becomes 'edda' (work of Norse literature).
'about' says the letters should be written backwards.
'r'+'edda'='redda'
'redda' back-to-front is 'ADDER'.
(Other definitions for adder that I've seen before include "One contributing more" , "Dread (anag)" , "Sliding" , "on country walks?" , "danger in the countryside" .)