In 1999 Duncan took the next step in his hockey career by earning a spot on the Penticton Pantheres (now Penticton Vees) of the British Columbia Hockey League at the young age of 16. Over an illustrious two year career, Keith finished with 78 goals and 148 assists for 226 points in 163 games.
After a stand-out junior career in Penticton, Keith was heavily recruited by various NCAA Division 1 schools finally choosing Michigan State University. As an 18 year old freshman, he played 41 games collecting 3 goals and 12 assists for 15 points. His first collegiate goal was scored in the Cold War – an outdoor game at Spartan Stadium against arch rival the University of Michigan. That summer at the 2002 NHL Entry Draft, Keith was selected in the 2nd Round, #54 overall to the Chicago Blackhawks. During his second season at Michigan State, he scored 9 points in 15 games before leaving for the Kelowna Rockets of the Western Hockey League. While with the Rockets, Keith netted 46 points over 37 regular season games with a +32 plus-minus rating adding 14 points in 19 games in the post season.