Kevin and his friends are venturing into adolescence as they find themselves staring at "Marsha Millany" in a bikini at the town pool. Winnie and Kevin survive a summer of "cross-town romance", Wayne has a car, and no one likes his new girlfriend Angela (Meredith Scott Lynn). To bring the family closer, Norma suggests going to Jack’s company picnic on Labor Day, but the outing isn’t as fun as they remember. Kevin finds out that the "office clown", Harry "Dead Wood" Detweiler (Rick Hurst) beat his father out of a promotion and is now NORCOM vice president while boating with his daughter Mimi (Soleil Moon Frye). In the softball game, Jack gets knocked out when Kevin accidentally hits a ball at him, but he is the one apologizing for not telling his son about the promotion. Wayne quickly gets dumped by Angela and wonders why. However, the family comes together in the end when they see Karen off to college.

As Kevin enters 9th grade, he has to make adjustments throughout his first day back. He has to deal without Winnie being there, his terrible class schedule, the return of bully Tony Barbella who takes his locker, a beautiful new girl Madeline Adams (Julie Condra), who’s quite the temptress when she kisses him; and worst of all, Becky Slater’s wrath. Becky blames Kevin for Craig Hobson breaking up with her before he went to military school. Kevin tries to get help from the school guidance counselor, but she’s away and Coach Cutlip is her replacement. His solution? Run laps!

Walter McCafferty (aka "Mr. Hormones") claims he is unofficially invited to Donna Pescarelli’s (Sarah Lundy) slumber party of 10th grade girls if they bring beer. Kevin and his friends decide to make the journey across town to crash the party, but their battle to get there turns into a war. Paul gets allergic to being in a different part of town, and Doug injures himself, forcing Randy to carry him the rest of the way. Then the mission is all but over when Walter gets caught taking beer by his mother and is grounded for the rest of the night, but Paul makes a speech that they must continue on without him.

After Paul complains about his $5 allowance, Kevin asks for a raise in his, but Jack says he has to earn the value of a dollar by doing chores around the house, earning only 50 cents more. Mark Kovinski (Justin Whalin), the "Howard Hughes" of RFK school, says he has two choices: be like his dad or be his own man, by caddying at the Whispering Green golf course. Kevin signs up for a golf caddy job in hopes of getting a $20 tip. There are three problems: the tip was earned by carrying a big bag, it belongs to his father’s boss Ken Stein (Alan Fudge), and Jack is playing with him. Ken is winning until he insults Jack for having cheap and old golf clubs, making Jack play better. He almost wins the game but deliberately misses an easy putt because he doesn’t like how his boss made Kevin fetch his club after throwing it in the lake. Kevin is thankful and treats him to lunch, realizing it is not so bad ending up like his father after all.

Winnie gives Kevin an ID bracelet for their one-year anniversary of him wanting to ask her out, but didn’t. Kevin gets partnered up with Madeline for a French cuisine cooking project in French class and has to spend an evening with her alone in her house making chocolate mousse instead of going out with Winnie. While there, Kevin accidentally leaves his bracelet—he gets flustered when Madeline says it wasn’t a coincidence that she picked him and tries to tempt him into tasting the mousse off her finger. At the movies with Winnie, Madeline sits behind them, but returns the bracelet by pretending she found it on the floor.

Now in 7th grade, Paul’s little sister Debbie (Torrey Anne Cook), who has a crush on Kevin, asks him to a cotillion dance when Paul weasels out of escorting her. Paul has "school spirit" on his mind by watching chesty cheerleader Dina Delgado (Stefanie Scott) with Randy and Doug at the Friday night football game. At the dance, Kevin feels out of place when he and Debbie are chosen to lead in the "Sweetheart Waltz". But when Debbie wants a souvenir pictures of their night, he ditches her for some fresh air. While outside, the guys break the bad news: something slipped from Dina’s sweater—she "stuffs". Heart broken over Kevin’s absence, Debbie finds him but her grandmother’s pearl earring accidentally falls in the pool. Playing hero, Kevin dives in to retrieve it, asks her to dance, and gets their picture taken together.

In the Arnold household, money is tight and things get worse when the stove stops working properly. At work, Jack asks for a raise so he can buy Norma a new stove. To his surprise, he receives it, along with a promotion as well, but it has a condition. Jack’s boss is forcing him to travel during Thanksgiving, which leaves Norma in charge of the Thanksgiving dinner. Jack might have to break tradition if he can’t make it home on time to carve the turkey.

It is "tryouts time" for the school basketball class and to Kevin’s surprise Paul is among the ones chosen. However, Kevin tries to prove to Paul that he’s not good enough to try out for Coach Cutlip’s team at school. But after 790 consecutive losses of backyard b-ball, Paul finally shows Kevin that things change when he wins one game. Paul makes the team after all and Kevin is his biggest supporter, cheering his buddy on.

While Christmas shopping with his mother, Kevin discovers that his gym teacher, Coach Cutlip (Robert Picardo), has another job as the Brightlin Mall Santa Claus. Back at school, Kevin is treated like royalty from the much kinder gift-giving "Ed" Cutlip so he wouldn’t give up his secret to the rest of the class, much to the annoyance of his friends. But Kevin accidentally tells Doug Porter he saw Cutlip working at the mall. Doug then tells Randy Mitchell, who tells Tommy Kisling (Jay Lambert), so they gather a mob to try to find the gym teacher there.

Paul nominates Kevin to run for the 1970 RFK Jr. High student-council president against his long-time nemesis Becky Slater. Paul then gathers Doug, Randy, and Tommy for his campaign team, but after three weeks of battling Becky at school with pranks, they’re no match for her and her highly organized team. Tommy tempts Kevin with a copy of Becky’s election speech. But after Paul introduces him as an honest and true every-man, Kevin’s conscience gets to him and he resigns from the race, losing the election.

When Kevin’s school holds a joint field trip to the Natural History Museum with Lincoln Jr. High, Kevin wonders why Winnie isn’t as excited as he is about spending the day together. At the museum, tensions rise when all Winnie seems to want to do is interact with her friends. Meanwhile, Paul, Randy, and Doug try to find the museum’s fourth floor where gangster John Dillinger’s remains are supposedly kept in a jar of formaldehyde. When Kevin gets lost, Madeline tries to make a move on him, but Winnie returns, creating an awkward moment. Kevin tries to explain that nothing happened, but Winnie confesses she’s met someone else and leaves. Kevin boards his bus and finds the ring he gave her there, and he begins to contemplate life without the "girl next door".

Days after the break-up, Kevin is still in denial over Winnie and cannot accept the fact she is with someone else, even when he is introduced to her new boyfriend, Roger. He plans to throw a party to get Winnie back and asks Paul to have the party at his house. However, Paul invites both Winnie and Roger. When Madeline talks to Kevin about the party, he asks her to go with him. At the party, Kevin tries to make Winnie jealous, and he ends up hurting Winnie more when he says their relationship didn’t mean that much to him. But he also tells Madeline to "get lost!" as well. With his heart broken, Kevin goes to Winnie’s house to apologize and to continue their friendship.

Grandpa Arnold arrives suddenly to attend the funeral of his cousin, Aunt Rose, a relative they hardly knew. At the wake, Kevin and Wayne meet their extended family, and are glad when they see Jack’s rich cousin Lloyd, who gives them $20 to split. After they argue over holding the money, it accidentally falls into Aunt Rose’s open casket. By the time they think of a plan to get it back, it’s too late and the casket is taken away for the funeral. On the way to the burial service, Kevin and Wayne bicker over the money and a furious Grandpa kicks them out of the car, forcing them to walk the last two miles to the cemetery. Once there, they realize why it was important to be respectful because even though they didn’t know their aunt, she still represented a part of the Arnold family heritage.

After a routine clean and check-up at the dentist, Kevin gets his first cavity and needs a filling; but feels embarrassed that he’ll wimp out in the presence of beautiful denial hygienist Miss Hasenfuss, and asks Dr. Tucker to make arrangements for Miss Hasenfuss not to be there for the filling. Hasenfuss is then replaced by the much older, crabby, and hoarse-voiced Mrs. Craw, making Kevin feel even more uncomfortable. But after he finds out that Miss Hasenfuss is taking his advice on going back to school to become a dentist herself, Kevin has the courage to ask her to assist Dr. Tucker one last time.

Kevin’s dog Buster is restless and will not stop barking, so his family leave it up to him to take him to the vet. But the veterinarian Dr. Ferleger’s suggestion of neutering chills the Arnolds to the bone and no one can decide whether to proceed. Meanwhile, Buster’s misbehavior continues when he chews up Jack’s important reports. Kevin takes Buster to the park, but he finds a female dog and runs away, leaving the family to search for him later that night. They soon realize that Buster is a part of the Arnold clan too—their faithful "silent partner".

After Norma finds a clothing sale advertisement in the paper, she urges Jack to take Kevin to the store, a one-hour ride away, to get him a new suit. However, due to Jack’s stubbornness to get directions, Kevin is unable to connect with his father and they miss the turnoff and get lost in the countryside. They stop at a diner where they find a cute waitress, but Jack embarrasses Kevin in front of her. They finally make it to the store but it is late and they are closing. In the carpark, they get a flat tire, leaving Jack and Kevin at odds with each other again. However, Kevin manages to get the jammed luge nut free and changes the tire by himself, impressing his father and restoring their ability to communicate.

Norma takes a job as a temporary secretary in the attendance office at Kevin’s school, making Kevin nervous about his school image. On her first day, during a fire drill, she also embarrasses Kevin by waving and saying "hi". As a result, Kevin asks her not to speak to him while at school, which she reluctantly agrees to. The next day, class bully Tony Barbella pressures Kevin to steal a green late pass, but Norma catches Kevin in the act and he leaves it behind. As a result, Norma is unable to work well and is fired. Later that night, however, Kevin notices her typing an application for entrance to Rider Community College.

Karen comes home from college for a mid-semester break and tells the family that she won’t be back for summer because she got a job on campus. Kevin and Wayne each want to have their own room, and begin to squabble over who has Karen’s room. The situation slowly becomes more heated, ending with Wayne preferring to sleep in his car rather than spend one more night together. Kevin, shocked by his brother’s comments, gets even when he kicks the bumper off Wayne’s car, accidentally causing it to roll down the street and crash into a hydrant. After the incident, they each admit wanting the room, but in the end, Jack flips a coin and Wayne is the one to go.

After covering for them while caught passing a note, the most popular students in school, Brad Patterson (Chad Allen) and Marci Doran, recruit Kevin to help with writing quotes in the yearbook. That night they ask him to provide a "funny" quote about an unpopular overweight classmate, Peter Armbruster (Michael Ray Bower), known as "Pig". In gym class, Kevin gets to know Peter and begins to feel guilty. He then asks to change his quotes, but it’s too late, and he gets called in to Diperna’s office and finds he has to take the blame. He later confronts Brad and Marci for selling him out, but realizes that they are untouchable and there’s more to life than being popular.

When Winnie shows up at Kevin’s house to "talk", he tries to chat but she is evasive. Kevin learns that Winnie broke up with Roger, and Paul thinks that she may want to get back with him. Later he meets her looking at her old house, but she isn’t interested in doing something together. At the skating rink, Winnie’s "distress" cannot be seen in front of her new friends—a couple of 11th grade guys. Realizing Winnie’s instability, Kevin tries to talk to her but she again evasive, wanting to forget the last three years. Later, Kevin learns that Winnie had a car accident. He leaves school and waits until dark for her, but her parents tell him that she doesn’t want to see him right now. He then sneaks back to see her later that night, and they mouth "I love you" through the window.

When Karen announces that she intends to moves into an old house that needs fixing up, Norma and Jack want to visit. But they are surprised when they meet Karen’s new roommate, who is actually her boyfriend Michael (David Schwimmer). Jack becomes irritated and questions his daughter’s values and the way she was raised. Meanwhile Kevin goes for a motorbike ride with Michael, and notices his love for his sister. Jack, after taking a walk, says he can’t tolerate this kind of relationship and demands she return to the dorms. Karen, however, defies her father and tells him that times have changed, even if he cannot.

As his junior high graduation approaches, Kevin learns from Winnie that Paul will be attending a prep school in the fall. Angry, Kevin confronts Paul, and makes fun of him, then punches him in science class, causing an explosion. Later, the pregnant Mrs. Heimer sees Kevin is troubled and offers him a ride, but their conversation is interrupted when she goes into labor, leaving him to drive her to the hospital. Kevin however makes it back in time for his graduation, and is taken by Paul’s speech about remembering their time as RFK Junior High’s class of 1971, and never forgetting the friends that were made there. That summer, Kevin patches things up with Paul, Winnie gets her cast off, and the three look forward to the future.

In a collection of flashbacks to past episodes, Kevin recalls significant people, places, and events in his life. The majority of them center around his family, his three years at RFK Junior High, his best friend Paul, and first love Winnie.