Kellen began his coaching career in 2007 at Northern Guilford High School as an assistant coach for the varsity women’s team. In 2016, he transitioned to the men’s staff as the head JV coach, and in 2019, he became the head coach of the men’s varsity team. During his tenure, he led Northern Guilford to back-to-back conference championships and earned Mid-State 3A-2A Conference Coach of the Year honors for both the 2019-2020 and 2020-2021 seasons, as well as All-Area Coach of the Year in 2020-2021.

From 2021 to 2023, Kellen coached the Pinecrest High School men’s varsity team, winning a regular season conference championship in the 2021-2022 season. He is now the head men’s coach at Robert B. Glenn High School in Kernersville, NC, where he led the varsity team to victory in the Frank Spencer Holiday Classic during his first season.