Unusual Taste in Sandwiches
Allison Reynolds (Ally Sheedy) embodies the Weirdo stereotype. She's likely the most enigmatic character in the movie. When she's dropped off, she turns to say goodbye to her father, but he just drives off. It helps foreshadow the point that she makes later, that she's unhappy because her parents ignore her.
At first, during detention, she doesn't talk at all. We see her doing unusual things like removing the cold cut from a sandwich and then replacing it with cereal and sugar from pixie sticks. She proceeds to eat it. Also, she draws a picture and then creates snow in the picture using her own dandruff. So, her behavior's kind of off.
But Allison eventually starts to say things. (She's also the only student who avoids smoking pot with the others.) She reveals that she's a neglected girl who has her own outlook on life. Allison's also adept at getting the others to reveal more about themselves: By pretending that she had an affair with her psychologist, she gets Claire to admit that she's never had sex (Allison's actually a virgin too):
ALLISON: I'll do anything sexual. I don't need a million dollars to do it either...
CLAIRE You're lying...
ALLISON: I already have... I've done just about everything there is except a few things that are illegal... I'm a nymphomaniac!
A Lot of Heart
Given her upbringing, Allison's feelings about parents and kids are sort of cynical. Yet, there's also a kind of sincerity and empathy underlying them. She wants to retain the passionate feelings of adolescence throughout her life and not give into numbness and middle-aged emptiness. She has this exchange with the others:
ANDREW: My God, are we gonna be like our parents?
CLAIRE: Not me… ever.
ALLISON: It's unavoidable; it just happens.
CLAIRE: What happens?
ALLISON: When you grow up, your heart dies.
BENDER: So, who cares?
ALLISON: I care.
Allison cares. She doesn't want to lose the magical warm-heartedness and humanity that supposedly attends your teenage years. She doesn't want to age into someone like Richard Vernon, who seems sort of arrogant and slickly villainous.
But despite the fact that Allison doesn't want to change, she actually undergoes a big change at the end of the movie. It's the most controversial part in the movie, actually. Allison and Andrew have started to hit it off, but in order for her to prove really attractive to Andrew, Claire needs to give her a makeover. She removes Allison's Goth-punk look, takes off her black eyeliner, and puts a bow in her hair. Andrew is smitten! They're gonna be together now! All she had to do was sacrifice her individual style and appeal to a more widely accepted image of sprightly young womanhood.
In a way, it's kind of like the end of Grease: In that movie, Olivia Newton John's character abandons her nice-girl style to become a leather-clad greaser-girl who will appeal to John Travolta's character. But be that as it may, Allison's presumably learned all the lessons that everyone else has needed to learn about getting along.
Then again, there's the possibility she didn't need to learn those lessons in the first place—she didn't have any friends before going to detention, but she says the kind of friends she thinks she might've had wouldn't have minded if she hung out with jocks and rich girls and criminals. She's very tolerant.