Though you grind a fool in a mortar with a pestle along with crushed grain, yet his foolishness will not depart from him. (Proverbs 27:22)
You can train a dog to do all kinds of tricks; you can dress it with the finest apparel, no matter what you do to it, it will remain a dog. Likewise, foolishness makes the fool. You and I cannot change him once his foolishness has permeated his being. There is hope however for the foolish child. "Foolishness is bound up in the heart of a child; the rod of correction will drive it far from him." Nevertheless once that foolishness has gone unchecked, it becomes one with its possessor. Do not think that you can change him. Do not hire him. Do not go into business with him. Do not date him and by all means, do not marry him. There is only one that can change the heart of a fool, Jesus Christ. Do not think that you can simply introduce him to Christ and he will be instantaneously changed. Maturity takes time, sometimes a lifetime.