Non-stop part of pretend lesson (7)
I believe the answer is:
endless
'non-stop' is the definition.
(I've seen this before)
'part of pretend lesson' is the wordplay.
'part of' indicates a hidden word.
'ENDLESS' can be found hidden inside 'pretend lesson'.
(Other definitions for endless that I've seen before include "Unceasing" , "Constant" , "Infinite, perpetual" , "without finishing" , "'Eternal, without finish (7)'" .)