Harris led Niagara to the 2005 New York State Class AA Championship averaging 19.7 points, 12.6 rebounds and 5.0 assists per game. He was recognized as the tournament MVP after scoring 19 points, along with eight rebounds and four assists in the championship match overcoming a broken thumb in his shooting hand.
Harris was named first-team all-state in 2005 as Niagara Falls finished 28-1 and third in the national USA Today rankings. He scored 24 points to lead the West to a 110-77 victory against the East in the 2005 Niagara PAL/ACE Showcase game in April and had 16 points for the Black Jerseys in the 2006 Jordan All-American Classic.
Harris found himself in trouble off the court however, facing minor drug and domestic violence charges for which he spent 13 days in jail.
Harris transferred to Notre Dame Prep (Mass.) before heading to college. While at Notre Dame Prep, Harris had 31 points in a matchup with Northfield Mount Herman, 26 points and 14 rebounds versus Blair Academy and 25 points against Winchendon School. He was a second-team member of the 2006 All-USA squad selected by USA Today.
Harris was a member of the USA Basketball Youth Development Festival squad that captured the gold medal at the 2005 International Sports Invitational. Harris tallied 28 points in the gold-medal game and led the seven-team field in rebounding average (9.0) and ranked fifth in scoring average (16.8).
The following year, Harris played in the 2006 Nike Hoop Summit game between the USA Junior Select Team and the World Select Team. He had a team-high seven rebounds and six assists, as well as six points in the 109-91 victory.