Hastened up with class report (7)
I believe the answer is:
narrate
'report' is the definition.
(thesaurus)
'hastened up with class' is the wordplay.
'hastened' becomes 'ran' (I've seen this before).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'with' says to put letters next to each other.
'class' becomes 'rate' (I've seen this before).
'ran' in reverse letter order is 'nar'.
'nar'+'rate'='NARRATE'
(Other definitions for narrate that I've seen before include "recount events" , "Tell story,recount" , "Tell us the story" , "Relate, recount" , "tell tales" .)