When Bart discovers that a fifth grader has a scar identical to one Bart has, Marge tells him about a club of four mothers she was in seven years ago; when Marge decides to reunite with the mothers, while Homer reunites with the fathers and Bart the boys, matters turn out much better for Marge than for Homer or Bart, who, after hearing the story from Jeffery Albertson about how they got their scars, tries to break up the group.
The episode opens with a dodge ball match between the 4th and 5th graders. Bart ends up hitting the last last fifth grader. However, Erik catches it after it comes back down, making the 5th graders win the match.
In the days that follow, the 4th graders harass the 5th graders to the point that they organize a fight after school. Before the fight begins, Bart notices Erik has a scar on his fist, which is identical to one that he has.
Bart confronts Marge about the scar. Marge explains that when he was in preschool, he was in a "Mommy and Me class" with three other kids. Marge became very close with the other mothers, and they became "the Cool Moms." However, the other kids were a bad influence on Bart. Marge then chooses to get back together with her old group.
Marge's old friends reconcile while Bart gets together with the other kids, where he realizes he still does not know where the scar came from. Marge and her friends chose to get together every Tuesday. Meeting with the other kids every week, their antics become more and more dangerous, so Bart plans to seperate the group. Knowing they broke up before, Bart realizes it must have something to do with the scar and consults Dr. Hibbert, who suggests he ask Jeffery Albertson. Albertson then reveals what happened: About seven years earlier, on the fourth of July, he was in charge of the fireworks. While Marge and the other mothers discussed this, Bart and the boys stumbled off towards the fireworks controls and pressed all the buttons, setting off all the fireworks. In the fiery explosion that followed, Albertson's sandwich was struck by a flaming ball, sending the burning hot skewers onto the boys fists, branding them.
Knowing it was an explosion that split them apart, Bart and Milhouse create a big ball of fireworks to break them up again. When Marge catches them in the act, Bart confesses. That evening, Marge tells the group of Bart's scheme to break them up, and they tell her Bart was always a bad influence to their kids. Marge becomes angry and leaves the group. Afterwards, the women all start making out with each other.