 In 1998, Yim began training at Charter Oak Gliders gymnastics club in Covina, California, and was coached by Beth Kline-Rybacki and Steve Rybacki.She quickly climbed the junior international elite ranks and won the silver medal in the all-around in the junior division at the 1999 U.S. National Championships after having placed 22nd the year before.She also won the silver medal on balance beam and on floor.