Rates some classes' sessions (8)
I believe the answer is:
assesses
'rates' is the definition.
(I've seen this in another clue)
'some classes' sessions' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ASSESSES' can be found hidden inside 'classes sessions'.
(Other definitions for assesses that I've seen before include "Carries out tests" , "Judges the worth of" .)