A link with the old school (3)
I believe the answer is:
tie
'a link' is the definition.
(I know that attach is a is a kind of of link)
'with the old school' is the wordplay.
'with' says to put letters next to each other.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'old school' becomes 'ie' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
't' put next to 'ie' is 'TIE'.
Can you help me to learn more?
(Other definitions for tie that I've seen before include "line above notes" , "Draw - knot" , "Fasten; draw" , "Attach, fasten" , "Neckpiece" .)