The beloved former teacher at Lakeview Elementary has married and moved on, so a substitute steps into the class: Miss Mildred Johnson Frances Rafferty. The new teacher immediately faces a skeptical crew of students led by the energetic William "Curley" Benson Larry Olsen, who and his friends are already plotting to push her out and return to fishing instead of lessons. They suspect Miss Johnson might be a bit odd, a half-mad eccentric who could never keep a rowdy class in line.
The county supervisor, Miss Payne Edna Holland, visits the school and learns that Mildred is actually Miss Johnson’s niece. With that revelation comes doubt about Mildred’s ability to control Lakeview’s spirited cohort, and Miss Payne voices her concerns about whether the young teacher is too inexperienced for such a challenge. Aunt Martha [Kathleen Howard] is nearby, offering support and a hint of family wisdom as Mildred tries to prove herself.
On the first day, Curley encounters Mildred on the walk to school and doesn’t realize she’s his new instructor. He explains the planned pranks aimed at a routine his class nicknames “Pigglepuss,” even describing a scheme involving his pet frog Croakey perched on a chair. He also confesses the desire to quit the teaching gig so the day can be spent fishing, revealing how deeply the kids’ minds are set on avoiding discipline. The real situation starts to unfold when Curley and his friends unleash a makeshift “rocketship” car powered by rockets and smoke bombs, aiming it through a classroom window’s exhaust tube. The car is soon hijacked by two troublemakers, Dis Rene Beard and Dat Donald King, who drive it wildly across fields and into a haystack, dragging the hay behind them in a chaotic, frightening ride.
Miss Payne arrives to respond to the danger and loses her composure, criticizing Mildred for what she sees as a lack of control. In response, Mildred redirects the focus from punishment to engagement, taking the children on a picnic with her Aunt Martha. She introduces the kids to baseball, football, and boxing, and she proposes after-school lessons as a reward for good grades, hoping to earn their respect and commitment rather than simply forcing obedience. The lesson isn’t easy, especially when Mildred ends up in a boxing exchange with Hank Gene Holland, a tough student who challenges her authority in the moment Miss Payne observes.
Curley returns from his hiding place and, misreading the scene, believes Hank is beating Mildred. He leaps into action, attacking Hank and sending him tumbling into a lake, a moment that leaves the class stunned and Curley mortified. The other students, grateful for Mildred’s patience and guidance, quietly acknowledge the change she’s bringing to the classroom climate. Miss Payne reassesses Mildred’s capabilities, learning more about her approach, and Mildred explains the earlier confusion: the smoky classroom wasn’t the fault of a deliberate prank, but the misdirected chase of the rocketship by Curley’s crew, and the way Dis and Dat ended up steering the situation out of control.
In the end, Mildred finds Curley hiding and crying, afraid of expulsion and the threat to her job. She reassures him with warmth and kindness—cake and ice cream—and, with a gentle victory smile, she retrieves Croakey the frog, signaling a new sense of steadiness and trust within the class. The film closes with a quiet acknowledgement that the substitute’s firm but compassionate approach has begun to reshape the school’s atmosphere, turning mischief into motivation and doubt into a willingness to learn, one lesson at a time.
