At the Leddy household in Annapolis, Md., Cameron hangs his sports trophies. In his first year of Taekwondo, the 12-year-old earned a spot in a national tournament this summer. Jonathan Hanson for The Wall Street Journal

How deeply Mom and Dad ought to invest in a child's athletic activities is controversial. Jay Coakley, a University of Colorado professor emeritus of sports sociology, argues that the less the better. Greater parental spending tends to weaken a child's sense of ownership of his athletic career, sometimes destroying his will to succeed, he says. "Kids are being labeled as burnouts when actually they're just angry at having no options in their lives," says Dr. Coakley.

Other researchers say heavy spending is problematic only if parents expect a performance-related return on investment. "When you take your kids to Disneyland, you hope it enriches their day—not that they'll win a competition to take Mickey Mouse home with them," says Dr. Dorsch, a former Cincinnati Bengals kicker who attributes his own athletic success in part to his parents' relaxed approach.

Mark Leddy says he tempers his expectations of his stepson's athletic participation. Mr. Leddy and his wife this year will spend almost $6,000—about 8% of their household income—on 12-year-old Cameron's Taekwondo lessons, competitions, purchases of apparel and equipment and travel to tournaments.

The Leddys require that Cameron participate in a competitive extracurricular activity. He is expected to work hard at it and do his best. His parents don't expect Cameron to win. And if he loses, he must do that with grace. "We know he's 12, but we tell him, 'You don't get to act like a child when you lose,' " says Mr. Leddy, director of publications for the Naval Academy Athletic Association in Annapolis, Md.

Cameron says he knows his Taekwondo costs his parents a lot of money. He doesn't think about it much, however, because they never bring it up. He says he appreciates the freedom to choose his own sport, encountering no pushback from his parents last year when he switched to Taekwondo from baseball. Far from feeling any pressure to win, the sixth-grader says that after losing he receives consolation from his parents. "My parents will bring out the positives, such as maybe I lost to a belt higher than me," he says.

In his first year in Taekwondo, Cameron earned a spot in a national tournament this summer in Florida, a trip he understands will be expensive. "The way we see it, just getting to the nationals is a win," says Cameron.

The Leddy approach may not be typical. In Dr. Dorsch's study, 163 sports parents, including 85 women, answered an online questionnaire about their income and the cost of their children's athletic endeavors. A majority—60%—spent less than 1% of gross income on their kids' sports, while 24% spent between 1% and 2%. Just 2% of parents spent more than 5% of income. The just completed study hasn't been published.

After their children completed a separate survey, researchers concluded that youth enjoyment and motivation declined as parental spending rose. In one case, a mother in a home with gross annual income of $200,000 reported spending more than $20,000 on her 18-year-old daughter's volleyball career. In turn, the daughter reported feeling a high degree of pressure (4 on a scale of 5) and low degree of motivation (2.5 on a scale of 5). "The more parents spent, the more the kids seemed to feel the pressure of doing well for Mom and Dad," says Dr. Dorsch.

In 25 years of coaching, Courtney Pollins, president of Big Apple Youth Football in New York, says he has found that parents who hire private coaches and buy the most expensive shoes "tend to be the same parents who are over-involved—yelling at the coaches and yelling at their own kids. I tell them to go home and not come back to practice."

Dr. Gould, of Michigan State, recently completed a review of the academic literature on parental involvement in youth sports. His finding: Young athletes thrive upon parental support—but only to a point. The review cites evidence that coaches may avoid young athletes whose parents take too active a role, and it makes mention of a study in which 13% of young tennis players reported that their parents had hit them after matches. One study mentioned by Dr. Gould suggests parents may want to invest in their own athletic pursuit: It showed that adolescents are twice as likely to play organized sports if their parents are physically active.

How about the parents of champions? A study of 10 U.S. Olympic champions found their parents exerted "little external pressure to succeed" while expressing faith in the child's ability and emphasizing "if you are going to do it, do it right," according to Dr. Gould's paper, which hasn't been published.

Dara Torres, a 12-time Olympic swimming medalist, figured her career might intimidate her daughter's swim coaches. So Ms. Torres vowed to keep quiet during the 8-year-old's practice sessions. But when Ms. Torres recently saw several swimmers on her daughter's team struggling to perform a drill without fins, she told the coaches that even elite swimmers don fins for that drill. "They're using fins now," says Ms. Torres, of Boston.

Write to Kevin Helliker at kevin.helliker@wsj.com