Speed, agility stack up to renown for Arlington Junior Olympics champion William Polly might look like any other 12-year-old kid among the throng of middle-schoolers who will swarm the halls of Jefferson Middle School in a couple of weeks. But the quietly poised young Arlingtonian is a Junior Olympics champion: an internationally renowned sport stacker. Sport stacking, which involves the timed stacking of plastic cups in specific sequences, has grown increasingly popular since the late 1990s, with more than 480,000 competitors worldwide. While competitors can range in age from 3 to senior citizen, the sport peaks young, between10 and14. The sport, which hones hand-eye coordination and agility, is taught in many physical education classes in public schools across Arlington County. William first started stacking in kindergarten, in an after-school program at Barrett Elementary. He got his first set of cups for Christmas in 2006 and started practicing in earnest in 2009. In April 2011, William won his first World Championship, becoming the youngest world champion and setting a world record. When sport stacking was added to the Junior Olympics, William became the first gold medalist. He has set 10 world records to date. The world champion's biggest challenge? Staying calm and stacking on. At the World Championships, everyone takes out their camera to film you. Then, someone on the other side of the room sets a record, and there's a lot of cheering. You have to set yourself off from everyone. You have to ignore your nerves," William says. William's parents say the sport has brought William confidence and poise. He can get up before a gymnasium full of kids to give a demonstration and not get rattled. I mean, the pressure of this sport is unreal," says Kris Polly, William's father. The astounding wins have brought William guest stints on "The Tonight Show with Jay Leno," "Live! With Kelly and Michael" and "The Steve Harvey Show," and trips around the world. He is gracious and modest as he shows a visitor around his room, whose walls are lined with trophies and photos from his tournaments, as well as a set of stacking cups bearing William's signature and his picture on a new tournament display timer box. He was featured along with other champion stackers in "Stacker," a documentary about the sport. "Stacker" was shown at the Arlington Cinema "N" Drafthouse in May to raise funds for Barrett and Jefferson schools. The family traveled to South Africa this summer, where William filmed a television commercial for a South African orange soda. That was his favorite trip because his family went on a safari together. Next week, the young Olympian (and his mom) will fly to Beijing to attempt to break his world record in the "cycle" stack on a Guinness Book of World Records television show. William shares his talent with other kids his age, visiting area elementary schools to teach and demonstrate the sport, advising those who want to start stacking clubs at school. He also likes to skateboard - to and from school - and play with a Rubik's Cube.