|Champion||Thomas Jefferson A|
|High scorer||Dwight Wynne, Capistrano Valley|
The 2003 High School National Championship Tournament was won by Thomas Jefferson A, consisting of "Adam Smith", "John Smith", "Joseph Smith", "Steve Smith", and "Tommy Smith," which were used as rotating pseudonyms for Sam Lederer, Jacob Oppenheim, S.R. Sidarth, Steve Young, and Will Sullivan. The tournament was hosted at the Myrtle Beach Convention Center in Myrtle Beach, South Carolina.
The tournament was formatted to be played by 64 invited teams, however two no-shows reduced the field to 62 teams.
As the initial field for the 2003 HSNCT consisted of 64 teams, the first six games were played according to a predetermined schedule in which teams with the same record would play each other. Due to two no-shows, several teams were credited with forfeit wins in the first six rounds, ensuring no school went winless. The remaining four rounds were power-matched with the stipulation that unlike in 2002, no team would play any other team more than once during the preliminary rounds. Since Maggie Walker (then Governor's School), which went undefeated in the preliminary rounds had defeated all one-loss teams as of round 7, their final three matches were against 5-2 Detroit Catholic Central, 6-2 Capistrano Valley, and 7-2 Dorman A. Other than this, no team played a game against a team with more than one game's difference in record, and teams eliminated from playoff contention were dropped to a second bracket so that already-eliminated teams would not eliminate teams still in contention. All teams with a 6-4 record or better advanced to the playoffs.
The playoffs were conducted via a double-elimination tournament, with the 24 playoff teams seeded based on their final rankings after the preliminary round. After the first game, the lowest seeded team still in the winner's bracket would play the highest seeded team left in the winner's bracket, the second-lowest seed would play the second-highest seed, etc., with a similar format for the loser's bracket. Once two teams were left, the last team left in the winner's bracket would play a best 2 of 3 advantaged final against the last team left in the loser's bracket.
Thomas Jefferson A defeated Dorman A 370-205 in the first game of the advantaged final. St. John's survived several close playoff games to finish in third place, while Walton finished fourth. The Small School Championship was won by Cutter Morning Star, who defeated Westmont Hilltop 250-220 in a one-game final, while Kent City finished third in the Small School division.
Top 12 teams:
|2.||Dorman "A"||8t.||Dorman "B"|
|3.||St. John's||8t.||Wilmington Charter|
|5.||Maggie Walker||8t.||Capistrano Valley|
Top 3 Small Schools:
|1.||Cutter Morning Star||13t.|
The top 10 scorers, based on points-per-20-TU-heard were named to the All-Star Team:
|1.||Dwight Wynne||Capistrano Valley||6.||Will Turner||Petoskey|
|2.||Jason Loy||Cutter Morning Star||7.||Zach Pozun||Westmont Hilltop|
|3.||Sean Hou||Fort Mill||8.||Pete||Detroit Catholic Central|
|4.||Slade Gilmer||Russellville||9.||Noah Rahman||Solon|
|5.||Joel Avila||Westminster Academy||10.||Jaline Gerrardine||State College|