 Although he was a member of the powerful Lamar Vikings teams of the late 1990s, he never started a game in his two years on the varsity team because he was considered too small (5 ft 8 in, 160 pounds) and too slow.He began his senior year as a third-string running back, and only after a knee injury to starter Justin Faust (headed to Stanford), was he elevated to second-string behind Tommicus Walker (headed to TCU).Also a standout sprinter, Jackson was a state-qualifier in the 100 meters and recorded a time of 21.78 seconds as a member of the Lamar 4 × 100 m relay squad, breaking the previous record.