You have to know that your dignity is no longer in yourself, but in your students.Share mistakes with him so that their mistakes can be corrected.Only by sharing their shame can we help them erase their shame.The best course that can be taken is the most natural one.As he should be at that age, frankly and directly, telling him the risks, pointing out to him clearly and sharply, without exaggeration, without anger, without being pedantic.And the most important point is, especially, you can't speak your opinion as an order, unless he has become only obedient to orders, or such an assertive tone is absolutely necessary.