I have a couple of students who are having extra tuition with a parent. This week one parent, after an argument with the son wanted me to confirm that as he was 'just' a passenger in the car it was o.k. for him to use his mobile?

No Sir, it is not o.k. for you to use your mobile while you are teaching your son, technically you, as the qualified driver is in charge of the car, therefore the same rules that apply to drivers apply to you.