High school graduation is finally here, prompting everyone to reminisce about how much their lives have changed over the past few years. Amy's relationships with Ricky and Ben weigh heavily on her mind, while Grace contemplates Jack's place in her life. Meanwhile, Adrian is ecstatic when an unexpected visitor knocks on her door.

Adrian meets Ricky's mom at the clinic and admits to her that she does not want to be a teenage mother but after talking, she has a change of heart and tells Ben that she will not go through with the abortion. When Ricky gets a call from Amy, he hangs up and Ashley receives a text message from Adrian, saying that she will have the baby. Ashley, therefore, tells Anne and George, and also attempts to convince her parents to withhold the information from Amy until after Ben tells her. When Ben and Adrian visit Grace to tell her the news, Tom overhears the conversation and relays it to Jack. Ben and Jack both tell Madison about Adrian's decision, and she attempts to tell Ben to tell Amy before anyone else does.

Ben decides to try his hardest to keep his secret from Amy and cut himself off from Adrian, but things become complicated when his father tells Adrian's father about the pregnancy. Meanwhile, Amy is pleasantly surprised to find that her family and friends are pushing for her to attend the music program in New York. Also, George and Anne continue to argue, specifically about some of Ashley's most recent decisions.

After Amy leaves for New York, Ricky moves into her house temporarily to take care of John, which doesn't please Anne and George, since something appears to be going on between Ricky and Ashley. Elsewhere, Adrian goes to her mother for advice on what to do about her pregnancy, and her parents' differing opinions threaten to split their family apart. Ben also wrestles with the reality of the situation and vows not to let it ruin his future with Amy.

Band geeks are spreading rumors through the school that Amy is pregnant again. Ricky is especially furious with these rumors and insists they aren't true. Later, when Ricky and Ashley are alone, they kiss! Ricky backs away and hurries out of the room. Meanwhile, in New York City, Bristol Palin shows up at Amy’s dorm room and Amy finds out that all of the girls in the music program are teen mothers.

After agonizing over the situation for far too long, Ben travels to New York so he can tell Amy about the baby before she hears it from someone else. Also, Ricky spends some time with his biological mother, who is 24 hours away from serving a jail sentence. Adrian spills the beans at school about her pregnancy in an unusual way, and Ashley thinks she might be in love with the wrong person.

While, Grace tries to find a boyfriend for Griffin, Ashley now has feelings for both Grant and Ricky.

Amy and Ricky continue planning their wedding, so Amy buys her dress at a thrift store. The dress is a little worse for wear, but only Amy sees the potential to make it great. Meanwhile, Ricky is upset about the dress and Adrian thinks the dress reflects her feelings about getting married.

Grace is struggling with what has happened, whilst Ben wonders what part he plays in Amy's new life.

Grace's love of self-love comes out at school in the form of a campaign called "Just Say Me". Which has girls all across school abandoning sex with guys in favor of a more personal activity that has the same end result. Meanwhile, Adrian's own campaign of trying to be Amy's friend bears fruit when Amy invites her over for a visit.

Amy goes on a date with Jimmy. Meanwhile, Ashley pursuades George to vist Anne to rekindle their relationship, and Griffin sends his cousin Grant to get to know Ashley. Ben visits Grace and tells her that he wants to be friends, and as he leaves, they kiss. At the same time, Amy and Jimmy kiss. After George knocks on Anne's appartment door, Josh answers and explains Anne is with Mimsy and might come back home. While Ricky encourages Amy not to get caught up with Ben and Grace, Adrain's parents tell her they will get married, therefore causing her mom not to take the job offer in New York. Anne tells Ashely that she doesn't think it would be good for her to return home.

Amy has not been taking anyone's phone calls for three days, and Ben is not handling it well, leading Grace to believe that she might have another chance with him. Meanwhile, George plans a romantic evening with Anne, and Ben accompanies Adrian to her first doctor's appointment. The tension continues between Ricky and Ashley, and Ricky approaches Ruben with a special request. Lastly, Amy contacts Adrian to offer her friendship and support.

Ben thinks Adrian is lying about being pregnant and doesn't act like himself. Elsewhere, Jack finds out his family is moving and thinks about not moving with. Also, Ashley has a talk with her doctor about birth control.

Amy learns she's doing poorly in summer school, so her dad tutors her and provides her with some life advice.

George gives Ricky and Ben some much needed advice. Ricky and Adrienne go to couples therapy and Adrienne shares a very personal story explaining why she wants commitment so badly. Grace continues to argue with her mom over dating so soon and decides she isn't ready for a serious relationship herself. When Anne goes into labor they come to the conclusion that they won't make it to the hospital in time so George, Amy, and Ashley are forced to deliver the baby at home. Adrienne and Ricky spend the night together and Ricky finally says the words Adrienne has been waiting to hear. Meanwhile, back at the Jeurgens household George comes to a shocking discovery about the baby.

In the fourth-season finale, Anne reveals some news to her loved ones. Meanwhile, Ben considers transferring to Dylan's school.

When Grace begins to pull away from everyone, Ricky takes it upon himself to try to help her out.

Jesse makes some decisions about his and Lauren's relationship, now that he is headed for college. Madison becomes interested in a new guy... her boss who is in his mid-20s. Grant tells Grace that he wants her to be tested for STDs before they consider having sex.

Ben and Dylan go on their first real date together. Elsewhere, Tom runs into problems with police.

Amy and Ricky's relationship grows increasingly strained when Amy decides she wants to tour a college in New York. Leo questions Ricky about his friendship with Clementine. Jack goes to extreme lengths to protect himself with potentially devastating consequences. Adrian is not happy when Omar goes on a business trip without her, especially when she learns that Amy is on the same flight. George's need to distance himself from Anne leads him down a new career path. Meanwhile, Cierra offers to tutor Ethan in math but his pride keeps him from accepting her help.

Adrian is devastated by Omar's decision and takes her pain out on Ricky and Jack. Ben refuses to give up on his dream of reuniting with Amy and makes a shocking confession to Alice. Ethan and Margaret have an honest conversation about his relationship with Kathy. Meanwhile, Clementine returns to town and pays Ricky a visit.

Adrian makes an attempt to get George and Anne reconciled, but only for her own selfish reasons.

Adrian and Amy's fighting escalates and Ricky intervenes.

Amy is jealous when Ashley gets her own room in the garage, while Ricky pursues Adrian but she claims to have moved on.

Mimsy returns, and a wedding is held.