Get pupils in order (5)
I believe the answer is:
'order' is the definition.
(I've seen this in another clue)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for class that I've seen before include "Opportunity to learn" , "Group of students" , "Elegance - form" , "Taste or style" , "seminar" .)