Category of schoolchildren (5)
I believe the answer is:
class
This clue could be a double definition.
'category' is the first definition.
(I know that category can be written as class)
'of schoolchildren' is the second definition.
The definition suggests a singular noun which matches the answer.
Can you help me to learn more?
(Other definitions for class that I've seen before include "School group" , "Opportunity to learn" , "Taste or style" , "High quality" , "Excellent" .)