After the death of efficiency expert Frank Gilbreth Sr., his widow Dr. Lillian Gilbreth has to raise their eleven children on her own with very little money. Declining cousin Leora's proposal to disperse the children among various family members, Dr. Gilbreth sends her offspring to Nantucket, accompanied by longtime family cook and handyman Tom Bracken, while she sets out to complete her late husband's lecture tour. Ernestine gets engaged to strapping frat boy Al Lynch. (Later, when Al comes for a visit, the rest of the kids, who do not like him, make it appear the entire family is nutty, so he breaks up with Ernestine. Ernestine is only briefly heartbroken.)
Dr. Gilbreth returns from an unsuccessful tour, and the family returns to Montclair. Anne Gilbreth, the eldest, meets handsome medical doctor Bob Grayson, whom she initially mistakes for a barber. The family works hard to make ends meet.
Sam Harper, of Harper Electric, comes looking for a couple of men trained by Dr. Gilbreth's late husband. Dr. Gilbreth offers to train some specifically for his company, as she and her husband worked as a team, but the chauvenistic Harper is uninterested. However, he changes his mind. Dr. Gilbreth talks him into sending her six students, instead of two. Harper provides four men and persuades two other companies to send a pair each. The school, located in her home, is a success.
Dr. Gilbreth is invited to give a dinner speech at the Engineers' Club of America in New York City, but when she gets there, she is informed there has been a mistake. They did not know L. M. Gilbreth was a woman; women are not allowed inside the club. She leaves a copy of her speech anyway, suggesting they have it delivered by a man. Driving home, she is so furious she accidentally runs into a parked truck and is hospitalized. Anne finds her mother under the care of Dr. Grayson. Initially mortified, she and the doctor eventually get engaged.
When Dr. Gilbreth tells Harper about the Engineers' Club fiasco, he decides to publicize her achievements, but the family are horrified when he makes them the subjects of a funny newsreel. Harper tells them it is all good publicity. Dr. Gilbreth is made a professor at Purdue University.
Meanwhile, Grayson becomes annoyed when Anne is reluctant to leave the family (or even tell her mother about their engagement), as she feels she is needed there. Dr. Gilbreth figures this out and talks Anne out of this odd notion. Anne leaves with Grayson for a position in Detroit.
That same night, Sam Harper tries repeatedly to talk to Dr. Gilbreth about something, presumably his feelings for her, but they are constantly interrupted. Eventually, she lets him know there is no room for anything more in her busy life, and he accepts it. The film ends with the university graduation of her youngest child.
This film is more true to the story than is the first film, Cheaper by the Dozen (1950). Only the 11 living children are featured, and Jane is accurately portrayed as the youngest after Robert. However, the real surname of Anne's future husband was Robert Barney, which is changed to Grayson in the film.[citation needed]
