One in class is an Einstein (6)
I believe the answer is:
genius
'einstein' is the definition.
(I know that einstein can be written as genius)
'one in class is an' is the wordplay.
I cannot quite see how this works, but
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
'class' could be 'genus' (I've seen this before) and 'genus' is located in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for genius that I've seen before include "Extremely clever person" , "Exceptional intelligence" , "great idea?" , "Bent" , "Exceptional intellect" .)