Born in Madison, Wisconsin, Tarpley grew up in Kalamazoo, Michigan, and attended Portage Central High School from 1998 to 2002. During her freshman season, she helped her school's women's soccer team reach the state semi-finals. In the following spring, she led her team to an undefeated season and the state championship. Against Bishop Foley Catholic High School in the final match, she scored her team's first goal and assisted on her team's other two, including the winning shot in the penalty shootout. She received several honors during her time there, including being named the 2002 Michigan Gatorade Player of the Year and the 2002 U.S. Soccer Chevrolet Young Female Player of the Year, in addition to being a 1999 NSCAA All-American and a Parade All-American in 2001 and 2002. She also played varsity basketball for Portage Central, starting at point guard during all four of her seasons.