Slocum started his coaching career as a volunteer assistant at Texas A&M, under his father R. C. Slocum. In 1990, Shawn served as a graduate assistant at the University of Pittsburgh, coaching the defense. He returned to coaching at Texas A&M, coaching tight ends, linebackers, and special teams from 1991 to 1997. From 1991 to 1993, Slocum helped the Aggies win three straight Southwest Conference championships. During the years 1994-97, he coached two all-Americans, Shane Lechler and Lombardi Award winner Dat Nguyen, who both went on to play for the NFL. During his seven-season coaching tenure at A&M, he assisted the Aggies to five bowl games, including four Cotton Bowl Classic appearances. The Aggie team record was 94-28-2 from 1991–1997. The 94 wins were the sixth in the country and also the greatest wins by any Texas Division I school in any decade. From 1998 to 1999, Slocum coached at the University of Southern California, where he coached Butkus Award winner Chris Claiborne, Zeke Moreno, and Markus Steele. He returned to A&M again and coached the Secondary and special teams from 2000-02. In 2005, he became assistant head coach and linebacker coach at Ole Miss, where he coached star linebacker Patrick Willis.