In high school, kids are acutely aware of winning, losing, and their own performance, and that can spell problems for good sportsmanship. "Whenever there is more pressure for results, that increases the chances kids are going to do what they need to do in order to win," says Joel Fish, PhD, director of the Center for Sports Psychology in Philadelphia. "They are more likely to cross the line, taunting another player or fudging a rule."
If a player makes a mistake, he often loses focus. "Success breeds confidence and vice versa," says Rob Gotlin, DO, a sports medicine specialist who directs several youth sports leagues, so positive reinforcement is still important now, as is a strong emphasis on discipline and values. Adults need to take the lead. "We need to teach from day one: When you step on the field, court, or pitch, you must have respect for the game and all the competitors equally, just like you see in martial arts with the respect for the dojo." Parents also need to watch their own mindset, says Dr. Gotlin, who is also the author of Dr. Rob's Guide to Raising Fit Kids. "Parents want to see their kid stealing a base or getting an extra hit. It's the adult world poisoning the kids' minds. We need to fix ourselves first and then instill values in our kids." The message you want to impart: "I am here to see you compete and work on your skills. Work on that during the match."
Emphasize what you can and can't control: Sportsmanship is a choice. "There are all kinds of forces out there that parents and coaches can't control," says Dr. Fish. "I can't control what ESPN says or what the other team is doing. But I can teach my kid the importance of playing by rules, shaking the hands of the opponent, helping him up if he falls—teaching him that even if his opponent doesn't do that, he can still do it because it's the right thing to do."

