Key from student class finally changing hands (7)
I believe the answer is:
seminal
'key' is the definition.
(seminal can mean influential or important)
'from student class finally changing hands' is the wordplay.
I cannot quite see how this works, but
'from' could be 'in' (I've seen this in other clues) and 'in' is located in the answer.
'student' could be 'ma' (someone studying for a Master of Arts) and 'ma' is found within the remaining letters.
The remaining letters 'sel' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for seminal that I've seen before include "Rudimentary, influential" , "Major" , "Having strong later influence" , "Original and influential" , "Groundbreaking" .)