Strictly Speaking:

One pupil who wrote ‘f*** off’ was given marks for accurate spelling and conveying a meaning successfully.
So much for the strict application of a point system in grading essays.
Or should the examiners institute a system of counter-points for disrespect and vulgarity?

‘It would be wicked to give it zero, because it does show some very basic skills we are looking for – like conveying some meaning and some spelling.’
If we're giving credit for skills that basic, then how about a couple of points for writing on the correct side of the paper. Or even for knowing which end of the writing instrument to apply to the writing surface.