Teachers do it for money (4)
I believe the answer is:
mark
'for money' is the definition.
(I have seen 'Old money' mean 'mark' so perhaps 'money' could also mean 'mark')
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for mark that I've seen before include "Take note of" , "The second Gospel" , "Brand - old German currency" , "Characteristic" , "Gospel writer" .)