What can we say about Sloane Peterson? She's a high school junior. She's a girl. She seems nice. She's a good dancer—you know, for the '80s.
Madam in the Middle
Sloane splits the difference between extremes. There's Ferris, an unrestrained pleasure-seeker who cares little for authority. There's Cameron, an anxious hypochondriac who's never met a rule he couldn't loathe himself for following. And then there's Sloane. Stable, thoroughly unmemorable Sloane.
What do we really know about Sloane? She's rich, but she's still nice. She's pretty, but she's still nice. She rebels against authority, but, you know, in a nice, ladylike way. But she's not too ladylike—she's still kind of one of the boys. Did we mention that she's nice?
This is Sloane, Ferris's… Whatever
Sloane seems like she's Ferris's love interest by default. We say "love interest" because it's never made clear what Sloane is to Ferris. We assume she's his girlfriend because Ferris talks of marrying her and expresses his anxiety over the fact that she still has another year of school left.
Then again, she's never actually referred to as Ferris's girlfriend. His dad doesn't recognize her in the taxi scene, and she and Ferris don't have a ton of interaction. We get zero sense of their history together. When Ferris sprints past some sunbathers on his mad dash to beat his parents home, he takes the time to go back and introduce himself to the girls. Not exactly a boyfriend move.
Seriously, Did We Mention That She's Nice?
The fact remains that Sloane's a girl, so she must be somebody's love interest, right? That's what the film seems to suggest by propping Sloane up as such a thin character. If nothing else, she's there to run interference between Ferris and Cameron. At the Von Steuben Parade, when Cameron thinks Ferris has ditched them and gets worked up accordingly, Sloane talks him off the ledge. So Sloane seems like a solid friend; beyond that, however, we don't know much about her.