At Fred MacMurray's insistence, all episodes were filmed out of sequence during the show's entire run using a technique now known as the MacMurray method. MacMurray would do all of his scenes in 65 nonconsecutive days. The cast regulars got haircuts once a week in order to maintain continuity. Guest stars would have to return months later to complete an episode. All kitchen scenes would be done together, then all scenes in the upstairs hallway would be filmed together, etc. This fact was well concealed until Dawn Lyn joined the cast as Dodie. Her upper front teeth grew in irregularly during the entire 1969-70 season, from being barely visible in scenes with MacMurray to being plainly visible in scenes without him. William Frawley never felt comfortable with this method of filming, having grown accustomed to filming "I Love Lucy" in sequence during its entire run.
Don Grady almost left the show when Tina Cole was cast as Katie. In an interview, Cole revealed that Grady felt she wasn't his type. As it turned out, they eventually fell in love in real life and almost got married not once, but twice.
When Barry Livingston first joined the show as Ernie, he replaced the character of Sudsy Pfeiffer as Chip's best friend. At that time, despite their noticeable age difference, both boys were in the same grade. However, once the character of Ernie was added as a regular to the series, he reverted to his actual age, three years younger than Chip, effectively establishing him as Chip's kid brother and in real life.
William Frawley really enjoyed working on the show and did not want to leave. To make matters worse, he was replaced by William Demarest, whom he hated in real life. Frawley would sometimes visit the set to see cast members and would frequently make suggestions for script changes as he used to do when he was on the show. Demarest finally stepped in and got him banned from the set.
The character 'Steve Douglas' was ranked #7 in TV Guide's list of the "50 Greatest TV Dads of All Time" (20 June 2004 issue).