Brilliant teacher turned up on time, which attracts interest (11,4)

'which attracts interest' is the definition.
(an outstanding debt might accrue interest)

'brilliant teacher' is the wordplay.
'brilliant' becomes 'outstanding' (I've seen this before).
'teacher' becomes 'debt' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'outstanding'+'debt'='OUTSTANDING DEBT'

'turned up on time' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.