[post_page_title]Christopher Castile – then[/post_page_title]
Christopher Castile played Mark Foster, who is Carol’s only son and the youngest of the Foster children. He is portrayed as a nerd and spends most of his time working with computers. As the show progresses, he becomes a more sociable character.
His first acting role was for the series, My Two Dads with fellow castmate, Staci Keanan. He appeared in a few small tv roles before being cast as a regular in Step by Step.