DeJean attended OABCIG High School in Ida Grove, Iowa. He played quarterback and defensive back in high school and holds numerous school records. As a senior, he passed for 3,447 yards with 35 touchdowns and rushed for 1,235 yards and 24 touchdowns. DeJean was the 2021 All-American Bowl adidas Player of the Year. In the state title game, DeJean made several impact plays as OABCIG defeated Van Meter. In a two minute span, DeJean recorded two tackles, returned a punt 14 yards, completed two passes for 52 yards, rushed three times for 22 yards and scored two touchdowns and a two-point conversion.
