On November 5, 2018, after skipping his junior year and a part of his senior year to play professionally, Ball joined SPIRE Institute and Academy, a prep school in Geneva, Ohio, where he played under head coach Jermaine Jackson.[28][29] SPIRE competed outside the jurisdiction of the Ohio High School Athletic Association, allowing Ball to play without concerns over his amateur status.[30] A number of prominent high school teams canceled their match-ups with SPIRE because Ball's professional experience would threaten their eligibility under their state federations.[31] His team was removed from the Hoophall Classic tournament because event organizers did not meet a $10,000 request from a Ball family associate in order for Ball to play.[32] On November 10, 2018, Ball debuted for SPIRE, recording 20 points, 13 assists and five rebounds in a 96–84 win over The Hill School.[33] On March 7, 2019, he scored 41 points, including 29 in the first half, in a 102–67 victory over Hillcrest Prep North at the Grind Session World Championship.[34] Ball helped his team reach the final and was named season MVP.[35] He was ruled ineligible for the 2019 McDonald's All-American Game due to his professional experience.[36]