Group of pupils showing high quality? (5)
I believe the answer is:
class
This clue is a double definition.
'group of pupils' is the first definition.
(school class)
'high quality?' is the second definition.
(I've seen this before)
'showing' acts as a link.
(Other definitions for class that I've seen before include "High quality" , "Type; social level" , "Body of students" , "Stylish; lesson" , "pupils?" .)