Healthy to go after top marks in addition (2,4)
I believe the answer is:
as well
'in addition' is the definition.
(I've seen this before)
'healthy to go after top' is the wordplay.
'healthy' becomes 'well' (similar in meaning).
'to' says to put letters next to each other (I've seen this in other clues).
'go after top' becomes 'as' (I can't justify this - if you can you should believe this answer much more).
'well' put after 'as' is 'AS WELL'.
'marks' acts as a link.
Can you help me to learn more?
(Other definitions for as well that I've seen before include "To boot" , "with equal effect" , "A swell sort of addition" , "Also, in addition" , "Also, additionally" .)