Garrett graduated from Seneca High School in Seneca, IL in 2006 where he was a multiple star athlete. At Seneca, his teams went 111-12 over 4 years as a Varsity Starter, two time 1st Team All-Stater, and won the 2006 State Championship by going 35-0. In 2014, his number, #33, was retired at Seneca High School. Garrett also started all 4 years at South Dakota State University in Brookings. He graduated ranked 6th on the All-time scoring list and 10th on the All-time assist list. In 2010, Coach Callahan went home and set up the Illinois Ambush Youth Basketball Academy. Later the Callahan's moved to Iowa where he started the Iowa Ambush Youth Basketball Academy. They now live in Sioux Falls, SD.
Personal: Garrett has an Bachelor of Science in Health Promotion. He is married to Beth and has two daughters and a son; Kinley, Raelyn & McCoy.
Favorite Quote: "Be more concerned with your character than your reputation, because your character is what you really are, while your reputation is merely what others think you are". - John Wooden