The magic word is negligence and the magic phrase is reasonable person.
If you act without being negligent in the manner that a reasonable person would expect you to act you have the basis of a defence.
If you act outside of any regulation, CAA, JAR, Club/School it may be used against you to support negligence.
My experience of the flying training industry (30+ years) is that negligence in many cases would be very easy to proove. So many schools /clubs seem to operate on a whim rather than any rules, and those who do never seem to take much notice of them.
Best example is that i had the sack for refusing to fly the schools aircraft that were not fitted with upper torso restraint. The school said they had a dispensation but a letter to CAA proved they had never applied for or been issued with a dispensation.
You can get personal liabillity insurance but do not know if you can get it for flying instructors.
TURBO--by the way how do you prove that the student has done those things when he is dead!