In 1935, Robinson graduated from Dakota Junior High School and enrolled in John Muir High School ("Muir Tech"). There he played on various Muir Tech sport teams, and lettered in four of them: football, basketball, track, and baseball. His older brother, Matthew Robinson, inspired Jackie to pursue his talent and love for athletics. Jackie played shortstop and catcher on the baseball team, quarterback on the football team, and guard on the basketball team. He was also a member of the tennis team and the track and field squad and won awards in the broad jump.
In 1936, Robinson won the junior boys' singles championship in the annual Pacific Coast Negro Tennis Tournament, and earned a place on the annual Pomona baseball tournament all-star team which included future Baseball Hall of Famers Ted Williams and Bob Lemon. The next year, he played for the high school's basketball team. That year the Pasadena Star-News newspaper reported on the young Robinson.