Sewell attended Riordan High School in San Francisco, California and was a student and a letterman in football.
Steve played three years of Varsity Football at Archbishop Riordan High School, he gained 1723 yards rushing in his career. In his senior year, he gained 1041 yards rushing and scored 10 TDs rushing as he led Riordan to an 8 win and 2 loss season.
Sewell played in 47 games in his four years with the Oklahoma Sooners rushing for 1178 yards and 10 touchdowns on 187 carries (6.3 avg) and also had 560 yards receiving and 4 touchdowns on 33 receptions (17.0 avg). During his senior season Sewell had 295 all-purpose yards in a 24-6 victory over conference opponent Kansas State; at the time it was the third highest single game total by a Sooner.