As an 8th grader, he won the 800 meter run and triple jump at the Andy Valley Middle School Championship.

[3] In high school, Harris competed for the Lewiston Blue Devils cross country and outdoor track and field teams.

[4] In his sophomore year, which was first cross country season, he finished 6th at the Maine Class A State XC Championships[5] with a time of 16:50.75.

A week later, Isaiah improved upon his personal best and state record by finishing 2nd at the New England Track and Field Championships[8] in a time of 1:53.35.

After finishing 2nd at the Maine State XC Championships in his junior year, he continued his dominance in outdoor track, winning every individual race he ran that season.