Down at the bottom of the class, nowadays (3)
I believe the answer is:
sad
'down' is the definition.
(I've seen this in another clue)
'the bottom of the class nowadays' is the wordplay.
'the bottom of' indicates one should take the final letters.
'nowadays' becomes 'AD' (AD, Anno Domini, as opposed to BC, Before Christ).
The final letter of 'class' is 's'.
's'+'ad'='SAD'
'at' is the link.
(Other definitions for sad that I've seen before include "low" , "grey" , "Heavy-hearted" , "Regrettable" , "Sorrowful, unhappy" .)