Student not so thick, having embraced reading? (7)
I believe the answer is:
learner
'student' is the definition.
(someone who is learning)
'not so thick having embraced reading?' is the wordplay.
'not so thick' becomes 'leaner' (lean means thin or narrow).
'having embraced' indicates putting letters inside.
'reading?' becomes 'r' (one of the traditional three R's of education).
'leaner' going around 'r' is 'LEARNER'.
(Other definitions for learner that I've seen before include "Pupil, novice" , "Acquirer of knowledge" , "Tyro" , "Amateur" , "Student (of driving?)" .)