Walker attended Rice High School in Harlem, New York City. During his junior year, Walker played once at Madison Square Garden against Simeon Career Academy and senior guard Derrick Rose in a 53–51 victory. Over his senior year, he posted 18.2 points and 5.3 assists per game, earning him a spot on the prestigious McDonald's All-American Team. He was able to play in the elite New York City Gauchos, the premier AAU basketball program for youth, and was joined by fellow Big East Conference talents-to-be Jordan Theodore, Darryl Bryant, Devin Hill, and Danny Jennings. Walker's team finished No. 1 in the nation.
