Although this isn't appropriate behavior, it's completely normal! Being smart makes no difference -- your son has found a strategy that he thinks works, and you need to educate him (probably hundreds of times) on strategies that ARE okay. First, give nurturing attention to the victim so that everyone sees that it's the injured person (not the misbehaving person) who gets attention first. Rather than reacting to your son's behavior with shock or emotional disapproval, get down on his level and calmly observe what you see. You can't reason with or teach a child who is having a tantrum, so if your child is pitching a fit, you can calmly say "I see that you are upset. You are scrunching up your face and moving your hands like this. You are safe." Once your son is calm (maybe he doesn't pitch a fit at all in these scenarios) you can calmly say "You wanted that toy, and you hit "Carlie" when he wouldn't give it to you. You may not hit. That is hurtful. When you want a toy that someone else has, you can ask this way: May I please have that truck? Try it now. Ask Carlie if you may have the truck. You did it! You used words to ask Carlie for the truck. Way to go!" Then you deal with whatever comes--if Carlie isn't ready to give up the truck, you talk about taking turns or finding something else to play with. Books that I highly recommend for parents and professionals working with kids (with normal age-appropriate behavior problems AND really serious problems) are anything in the Love and Logic catalog and also Becky Bailey's Easy to Love, Difficult to Discipline. These are great books that teach you great strategies not only for helping your child but for helping yourself manage your own stress. They are fun and easy to read. Good luck! If you are calm and take an educational stance, the biting/hitting phase will pass!