Classic that will be read in language lesson (7)
I believe the answer is:
ageless
'classic' is the definition.
(I've seen this before)
'that will be read in language lesson' is the wordplay.
'that will be read in' indicates the answer is hidden within the clue.
'AGELESS' can be found hidden inside 'language lesson'.
(Other definitions for ageless that I've seen before include "Eternal - like Peter Pan" , "Lasting a long time" , "Forever young" , "Never appearing to grow old" , "Always youthful" .)