Their function is to secure quiet in class (6)
I believe the answer is:
'their function is' is the definition.
I can't tell whether this defines the answer.
'quiet in class' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'in' indicates putting letters inside.
'p' placed into 'class' is 'CLASPS'.
'to secure' is the link.
Can you help me to learn more?
(Other definitions for clasps that I've seen before include "Holds tightly" , "Embraces; fastenings" , "Necklace fasteners" , "Fasteners, as on necklaces perhaps" , "Embraces, hugs" .)