Fleming attended St.Rita High School in Chicago, Illinois. As a junior, he recorded 105 tackles including 15 tackles for loss and nine sacks, and helped lead St. Rita to the Class 7A state championship. As a senior, he led his high school to the Chicago Prep Bowl city championship. He recorded 69 tackles including 15 tackles for loss and ten sacks. For his efforts, he was chosen to play in the U.S. Army All-American Bowl in San Antonio, Texas.