He compiled a 555–302 record in 34 seasons as a head coach, including an NCAA Division III National Championship with Calvin in 1992.
He began his coaching career at Shelby High School, where he won two state championships behind star Paul Griffin.
At Calvin, Douma made the Knights one of the most consistent teams in the Michigan Intercollegiate Athletic Association (MIAA).
In the 1991–92 season, Calvin went 31–1 and won the program’s first national championship and Douma was named NABC Coach of the Year.
He returned from retirement a second time to serve as a volunteer assistant for his former player Bill Sall, at Ferris State from 2009 to 2014.