 Okongwu attended Chino Hills High School in Chino Hills, California and started on the varsity basketball team since his freshman season.In his first year, he was teammates with brothers Lonzo, LiAngelo, and LaMelo Ball, who helped elevate the team into the national spotlight.His team ranked number one in the country with a 35–0 record and captured the California Interscholastic Federation (CIF) Open Division state title.