Wish Upon a Star is about two high-school-age sisters with extremely different personalities, who magically exchange bodies with each other for a while, and come to realize what an incredibly bad idea it is to be anyone other than oneself.Alexia (Katherine Heigl) is older and taller. She is socially popular, but she is also dishonest, vain, extravagant, lazy, an "airhead", and a bad student. She hangs out with a clique of obnoxious, cruel, arrogant, and snobbish friends -- Kazumi (Jacque Gray), Talley (Kari White), and Sabrina (January Sorensen). Her breakfast table reading is Self Magazine. She has a boyfriend Kyle (Donnie Jeffcoat) who is actually a decent guy.Hayley (Danielle Harris), the younger one, is a geek and a good student, interested in science and math. She has for some time been working on a science fair project, a lantern that uses discarded fruit as its energy source. She and her friend Caitlin (Ivey Lloyd) are both very shy. She has no boyfriend, and secretly covets Alexia's boyfriend Kyle. Her breakfast table reading is Scientific American. But she and Caitlin are not blameless -- They like to read Alexia's diary, and try on her expensive and stylish clothes, after school when Alexia is out with Kyle.Their father Ben (Scott Wilkinson) and mother Nan (Mary Parker Williams) are both practicing clinical psychologists. In spite of the wisdom that this ought to have conferred, they are both comically and utterly clueless and oblivious about their daughters' behavior. They decide early on that taking a "hands off" attitude is the way to deal with the girls' sibling rivalry and Alexia's provocative clothing. If there are no rules, misbehavior will be impossible. Because of this detachment, they never figure out what is going on when the girls switch personalities. Their breakfast table reading is things like Psychology Today or Nature Conservancy.One night, while Hayley is out on the porch stargazing with a telescope for her astronomy homework, she glances down at Alexia and Kyle in the hot tub. A meteor (shooting star) crosses the sky. Hayley makes a wish to be Alexia.The next morning, they wake up in each other's bodies and each other's bedrooms. They stumble around a bit in their unfamiliar rooms, and go into their bathrooms. Alexia, now in Hayley's body, notices it first. She sees herself in the mirror and screams. Hayley, now in Alexia's body, comes in. They both scream at each other. When they are able to talk, Hayley-in-Alexia's-body says:"Man, oh, man, it worked!""What worked? You did this?""I made a wish when I saw a shooting star. I didn't think it would work."She brings her hands up to feel her now-larger breasts. (It's completely decent; they are both wearing night clothes. But the Disney broadcast cut out a couple of seconds here.) Alexia-in-Hayley's-body slaps the hands away. She demands that Hayley switch back, which Hayley can't do (it's daytime) and wouldn't do in any case. Alexia leaves the room. Hayley, now in Alexia's body, looks at herself in the mirror. She is delighted. Alexia has no choice but to go to school as Hayley. Hayley has an astronomy test, which Alexia can't possibly take because she is such a bad student. They decide that Alexia-in-Hayley's-body will faint and be taken home, and make up the test the next day after they have presumably switched back.Hayley nearly trips and falls while coming downstairs; she isn't accustomed to her taller body. They drive to school as usual, except that Hayley doesn't know how to drive, so Alexia has to. When they arrive, the principal Ms. Mittermiller (Lois Chiles) sees what appears to be Hayley in the driver's seat, and chews them out for this. During the astronomy test, Alexia-in-Hayley's-body faints, as planned, and is taken home by her mother.At lunch, Hayley-in-Alexia's-body invites Caitlin (her actual friend) to join her and her clique for lunch. Caitlin is astonished at being let into this clique. The other people don't see anything wrong, except for the strange invitation to invite Caitlin. It then comes out that Alexia had split up with Kyle the previous night in the hot tub. These people have an arcane set of rules, one of which is that one is not allowed to go out with any one boy for more than three months, and the clock was up last night. She was supposed to call Kyle a "sick puppy" and send him on his way. Hayley-in-Alexia's-body is horrified. She runs over to where Kyle is. Kyle is hostile. She says "Whatever I said last night I didn't mean. I wasn't being myself." She wants to go for a walk with him after school. He says "I'm not interested in going with someone who calls me a sick puppy." She finally persuades him to get together after his basketball practice, and they can talk, and she can give him a ride home.Meanwhile, back home, Alexia is eating ice cream and watching music videos. Their new neighbor Simon (Matt Barker) comes over to give her some cookies. He has noticed Hayley and likes her. But this is actually Alexia, and she doesn't know who he is. He is puzzled by this.The time has come for Hayley-in-Alexia's-body to give Kyle a ride home. She has an extremely hard time driving; she never learned. After she goes up on the curb and nearly has some accidents, Kyle takes over the driving. They arrive at Kyle's house. She tells him that he is the most gorgeous guy she's ever met. He tells her that he really likes her, and thinks that she is beautiful, especially now that she isn't wearing so much makeup. She wants him to say that he loves her. He doesn't want to do that, but he says that he really really likes her, and wants them to be together. They do a lot of kissing, over Mozart's sensuous Elvira Madigan Concerto on the car radio (Hayley likes classical, Alexia likes rock.) This is a first for her; she has gotten her wish.When she gets home, Alexia-in-Hayley's-body is already eating dinner. Hayley sits down, and Alexia notices that she has a hickey on her neck from the kissing. She drags Hayley into the kitchen."That's a hickey, you tramp! Who did this?""Kyle. We were kissing.""I broke up with Kyle last night.""Well, you got back together with him this afternoon."Alexia drags Hayley into the backyard and yells at her."You mean to tell me that I'm stuck in this measly little body for another day, while you just parade around, ruining my reputation?""Looks that way, doesn't it?""That's it. This is war!"The next morning, the war begins. Alexia-in-Hayley's-body has hung a threatening note over Hayley's bed. When Hayley comes downstairs, she sees that Alexia is wearing an extremely provocative dominatrix outfit. Their parents make no attempt to stop this. Hayley goes back upstairs and dresses as a complete slob. She goes out to drive to school, without taking Alexia. Simon asks for a ride, and she gives it to him. Her driving skills are improving very slowly.Meanwhile, Alexia-in-Hayley's-body goes to school with a boombox and a tape of seductive music. At various times each of them writes an insulting graffito about the other on the restroom wall: "Hayley/Alexia Wheaton is a wench." The photographs of the candidates for Queen of the upcoming Winter Festival are taken that day. Alexia is in the running, and she (that is, Hayley) deliberately "bombs" the picture.It's time for Hayley to make up the astronomy test. It's really Alexia, and she is willfully rude and uncooperative, to the disgust of the teacher, Mr. Frauenfleder (Dane Stevens).At lunch, Alexia-in-Hayley's-body gets up on a table, takes off her jacket to reveal the dominatrix outfit, puts on the boombox, and performs an incredibly raunchy and risque song and dance. (This was almost completely censored in the Disney version.) Caitlin is horrified to see her friend acting this way. To retaliate, Hayley-in-Alexia's-body grabs Kyle, brings him right in front of her sister, and starts violently kissing him, saying "Oh Kyle, you're such a good kisser. Give me another hickey, baby." Ms. Mittermiller arrives and puts a stop to everything. She takes the girls into her office. They are totally unrepentant and disrespectful. She tells "Hayley" that this is grounds for disqualification from the science fair, threatens "Alexia" with suspension, and says that she will meet with their parents the next day. She then takes them both into the ladies room and tells them to clean up the graffiti. After Ms. Mittermiller leaves, Hayley-in-Alexia's-body says:"I can't believe you would do that. I've been working a year on that [science fair] project.""If I could have, I would have had you expelled too. I mean at first you come home with a hickey on your neck. Next you're practically mauling my boyfriend in the cafeteria. What next, Hayley? Are you going to lose my virginity too?""You--You're a virgin?""Yes, I'm a virgin!!! I have morals, Hayley! You obviously don't know very much about me.""Wow. I mean, Caitlin and I were sure that you and Kyle were---Well, I didn't do anything like that, except kiss. A lot.""You didn't?""I can't believe you actually thought I would do that.""What am I supposed to think?""I'm sorry, Alex. I'm really sorry."They both see that what they have been doing is wrong. They reach an understanding that they will help and support each other, and will switch back as soon as possible.That night, they plan to see a shooting star and reverse the wish. Before doing that, while lying on a blanket in the backyard, they talk. Alexia-in-Hayley's-body assures Hayley that she, Hayley, is good-looking and can get a boyfriend; she just needs social confidence. She should approach Simon. They agree to put off the switch one more day, so that Hayley can gain more social confidence in Alexia's body, and Hayley can use her intellect to show Alexia's teachers that she is not an airhead.The next day, the threatened conference between the school principal and the girls' parents takes place. Ms. Mittermiller tells them in no uncertain terms how shocking the girls' behavior had been in the cafeteria. The parents explain their "hands off" theory of upbringing, that they are allowing the girls to do anything they want, and that they consider this a positive innovation in parenting. Ms. Mittermiller is left speechless. After the parents leave, she mutters to herself "Those poor girls."In a math class that both sisters are taking, the teacher Mr. Watson (Mark Hofeling) asks for a volunteer to work out a practice problem for an upcoming test. Hayley-in-Alexia's-body volunteers. Mr. Watson is initially skeptical, because Alexia is such a bad student. He finally lets her come to the whiteboard and do the problem, which she (Hayley) does superbly.Hayley-in-Alexia's-body goes to hang out at Kyle's basketball team practice. Kyle is very happy; he will be starting on the team for the next day's game, and then Alexia will be crowned Queen of the Winter Festival, and they will dance the night away. He tells her that he loves her. Hayley is in an impossible position. She says "You shouldn't have said that to me. I've got to go home. The next time you say it, you know, the 'L' word, if you decide you still feel that way, pretend like it's the first time." She runs off, leaving Kyle bewildered and heartbroken. She goes out to the parking lot, where Simon asks her for a ride home. He gives her a box of chocolates, and gives her a quick kiss on the cheek. They drive off. Kyle sees the whole thing from behind the door.While they are driving--Hayley's driving skill has significantly improved by now--Simon apologizes for the kiss, and tells Hayley-in-Alexia's-body that he really likes her. Not for her looks, but for her personality. He says that he had had a crush on Hayley at first, but that he and "Alexia" are personally compatible. "Wait. You're talking about Hayley? You think Hayley's attractive?" Simon tells her "It's what's inside that really matters." She is absolutely delighted. Simon likes Hayley, body and soul, for who she really is. She says "Look, Simon. I think you need to get to know Hayley better. We're sisters. We're a lot more alike than you think."That night, the weather is clear, and they plan to stay up and do some star-gazing. But they both fall asleep in the living room, and their parents find them and put them in their beds. But in the middle of the night Hayley-in-Alexia's-body wakes up, realizes what she has to do, goes out onto the balcony to watch. She sees a shooting star and makes a wish to be Hayley again.Unfortunately, the next morning, nothing has changed. Hayley realizes that the change is apparently irreversible. She is ruined. She will spend the rest of her life as someone other than who she is. She doesn't tell Alexia what happened. Adding to her grief, today is an important day for both of them. Her sister will be making the presentation, for the science fair committee, of the project that she had worked on. And the admissions committee of Felder College, that Alexia wants to get into, will be interviewing her, as Alexia. That evening will be the big basketball game and the Winter Festival. At lunch, Hayley gives Alexia some last-minute coaching on how to explain the workings of the distillation process in the lantern. Then they see some flyers that are being distributed, inviting the whole school to a party at Caitlin's house. They are sure that Caitlin would never have done that. It was perpetrated by Kazumi, Talley, and Sabrina. Caitlin had thought they were her new friends, and had simply invited the three of them over for dinner. Alexia and Hayley both go to confront them. Caitlin is in tears. Alexia-in-Hayley's-body takes Caitlin away, while Hayley chews the the three of them out, and demands that they apologize to Catlin. They refuse to do so. Hayley-in-Alexia's-body says that, if they exploit gentle people like Caitlin that way, they are not worthy of being her friends any more. She leaves. She then has one more difficult encounter with Kyle, reminding her of how totally she has messed up her life.Alexia gets through the science fair presentation successfully, and Hayley gets through the college interview successfully. The home team wins the basketball game.Before the Winter Festival itself, Alexia-in-Hayley's-body goes searching for Hayley, and finds her, brooding by herself, in the grandstand of the swimming pool. Alexia shows off the new dress she has bought. She of course got it for Hayley herself, for after they have switched back. Hayley asks:"Do you like it?""Of course.""Could you live your life like that?""Sure, but that's irrelevant. We're going to switch back."Then Hayley tearfully explains that the change is irreversible. They can't switch back. She tells Alexia that she had gone out on the balcony the previous night, seen a shooting star, and made a wish. And nothing happened. Alexia then explains that, back when she was in the hot tub with Kyle, she had seen the same shooting star, and made a wish to be Hayley. "Why would you wish that?" "There I was, this C-minus student, about to break up with my boyfriend over some self-imposed rule. I felt totally bored with myself, and my friends, and everything. I realized that I didn't have much of a shot at getting into college. And I look up on the balcony and I see my brainy, adventurous little sister, with all these interests, like conserving energy. And I knew you would never make the same mistakes I made." They come to the realization that the wish only works when both people make it. They run out to the athletic field for some star-gazing. The heavens oblige them, they make the wish, and they switch back.They go back inside, where the Winter Festival is going on. Alexia's three friends come by, and tell her that they have decided to abolish all the funny rules, except for number 9, the one that says they will be friends forever. She then finds Kyle, and says "Just give me one more chance, please?" "What about that other guy I saw you with?" He is referring to seeing Simon kissing her, but she knows nothing about this; she wasn't there. She says "There's only one guy for me. I love you." "I love you too, Aly." Alexia almost misses the announcement that she has won the vote to Festival Queen, because she and Kyle are kissing.Then Hayley finds Simon, and says "Look, Simon. I know you haven't gotten the best impression of me so far. So let's start over." Simon replies "Alex did say I should get to know you better." The two sisters are finally in the right bodies dancing with the right boyfriends.
Output: Question: How old are Alexia?, Answer: 18