Smart attended Scotlandville Magnet High School in Baton Rouge, Louisiana and led the school to a state title as a freshman, earning MVP honors. As a sophomore, he averaged 22.4 points, 7.2 assists, and 6.9 rebounds per game. He participated in the Under Armour Elite 24 Showcase in August 2016. As a junior, Smart averaged 25.1 points, 8.7 rebounds, 6.4 assists and 2.1 steals per game. He was named Gatorade Louisiana Player of the Year for the second consecutive season and led Scotlandville to a state title in 2017. As a senior, Smart averaged 32.9 points, 10.6 rebounds, and 6.1 assists per game, sometimes playing the center position. He led the team to a state title and was again named Player of the Year. Smart was considered a five-star recruit and was ranked 21st in his class according to 247Sports. Smart committed to LSU over offers from Kentucky and UCLA.
