Screwcutting :S
Go away and read about it, its not overly difficult if you're confident with the lathe (and you must be by now if youve got it mostly finished). 2 things to note about it:
1. Take your time over setup, getting the tool at centre height and square to the work, checking the changewheels/QC gearbox are set right, check the work is running true.
2. Take your time when your cutting, small cuts avoid the tool springing, and avoid the work ending up in the scrap bin.
Yeah, your teacher is right, it isnt standard GCSE stuff, but if you can do it, it should impress the examiner :P
Edd :P