Klassen was a clever playmaker for the WHL's Saskatoon Blades from 1970 to 1975. He was regularly among the league leaders in assists while finding the net himself on occasion. In 1974-75 he was a member of the Western Canada all-star squad that represented Canada at the 1975 World Junior Championships. Later that year he was the top scorer in the post-season as the Blades narrowly lost to the New Westminster Bruins in the league championship series.