Isaac first attended Barron Collier High School in Naples, Florida during his freshman and sophomore years. In his junior and senior years, he attended the International School of Broward in Hollywood, Florida. However, as a result of wanting to be reclassified as part of the high school class of 2016, Isaac also attended IMG Academy for what was considered to be a postgraduate year in 2016. As a senior in 2016, he averaged 17. 6 points per game and 10. 0 rebounds per game while leading IMG Academy to a 21-10 overall record. In his high school career, he grew six inches from his freshman year to his senior year, going from a combo guard of sorts to the combo forward he is today. Issac was selected to play in the 2016 Jordan Brand Classic and Nike Hoop Summit All-Star games. Isaac was rated as a five-star recruit and ranked as the No. 12 overall recruit and No. 4 Small forward in the 2016 high school class. On July 5, 2015, Isaac confirmed that he was going to commit to Florida State after his senior year of high school ended.