Cool drink to quickly follow extra lessons (9,6)
I believe the answer is:
refresher course
'follow extra lessons' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'cool drink to quickly' is the wordplay.
'cool drink' becomes 'refresher ' (I've seen this before).
'to quickly' becomes 'course' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'refresher'+'course'='REFRESHER COURSE'
Can you help me to learn more?
(Other definitions for refresher course that I've seen before include "study update" , "further education?" , "Training" , "it helps you get up to speed" , "sweet group?" .)