On April 21, 2015, Thornton committed to play college basketball for Duke over offers from Arizona, Kentucky and Louisville.[3] Coach Mike Krzyzewski convinced him to reclassify to the 2015 class to replace point guard Tyus Jones, who was leaving to play professionally. Thornton was a consensus five-star recruit and one of the highest ranked point guards in his class.[2]
College career
As a freshman at Duke, Thornton made 20 starts but saw his playing time fluctuate despite being the only pure point guard on the team. He averaged 7.1 points and 2.5 assists per game.[4] Following the season Thornton transferred to USC, choosing the Trojans over Kansas, Washington and Miami.[5] After sitting out a season as a redshirt, he averaged 3.8 points and 1.2 assists per game off the bench. As a redshirt junior, Thornton started 27 games and averaged 7.7 points and 4.3 assists per game.[6] He opted to transfer after the season as a graduate transfer and committed to Boston College after considering Gonzaga, Texas Tech, Auburn and St. John's.[7] Thornton averaged 12.7 points, 2.8 rebounds, 3.4 assists and 1.1 steals per game in his final season at Boston College.[8]