[Quinlan]

I agree it is very rare to have an actual crash. When the occasional spin happens it seems it is often due to either the student trying to chase a faster car/driver (as was said above), or the student is trying to pull away from, or keep in front of, a faster car/driver that has come up behind him.
I think the vast majority of people who track cars would qualify as "type A" individuals, so the competitive nature is hard to keep in check.

Unless there is a weather factor or fluid on the track, a spin or crash when the student and instructor are away from traffic is very very rare.