When the series was casting its characters, child actor Jarrett Lennon originally landed the role of Mark Foster. Lennon had been chosen by the producers after guest starring in the last original episode of the Miller-Boyett series "The Hogan Family", which was produced in late 1990. After shooting the original (unaired) pilot for "Step By Step", Lennon was dismissed from the role of Mark, and the producers later replaced him with Castile (who had blonde hair like on-screen mother Somers, as opposed to Lennon having brown hair). Most of Lennon's pilot scenes were reshot with Castile, but during the first season, footage of Lennon remained in the show's opening title sequence. Lennon only appeared in wide shots with the Lambert/Foster family or, in the case of Suzanne Somers' credit scene, fleetingly appearing at the bottom of camera view as the kids huddled around Somers. All traces of Lennon were edited out by the second season. In 1996, these two actors had the tables turned on each other; Castile served as the original voice of Eugene Horowitz on the Nickelodeon animated series "Hey Arnold!", but after a few episodes was replaced by Lennon, who voiced Eugene for the remainder of the show's first season.