Head of the class (4,5)
(Another definition for star pupil that I've seen is " best in class?".)
'head of the class?' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dean that I've seen before include "One is in charge of a university department" , "James ..., film star famous for his moody rebellious roles" , "Administrator of a college department" , "Small valley - cathedral dignitary" , "Jonathan Swift's occupation" .)