Jeanie makes no sense (Ferris couldn't get away)
So, Jeanie almost drives right INTO Ferris, while having her mom in the car.
What does she do? Squint her eyes and hit the gas, INSTEAD of the obvious, "Look, mom, it's Ferris!".
Which is more realistiC? Which would ACTUALLY happen in that situation? She WANTS Ferris to get caught, and yet rather 'races him home' instead of a simple "Look, mom!".
Also, why doesn't 'mom' see Ferris? Usually when you're sitting right next to the driver, you see the whole road pretty clearly, if the car is about to hit something and the driver has to break really hard to avoid hitting it, the passenger is 100% aware of what it was and what was going on - at least as much as the driver.
My point is, the mom should've seen Ferris at least as much and as well as Jeanie. Why wouldn't she? She would be interested in her daughter's driving skills and development, she would be judging and evaluating her daughter's driving, so she can help her and make her a safer driver - an experienced adult's perspective is always useful for a relative beginner (which we have to assume Jeanie is when it comes to driving).
Why would she NOT be looking where she's going and so on?
In any case, ALL she had to do is say "Look!", just one word, one utterance - just open the car door if you have to and shout "FERRIS!!" or whatever gets the mom's attention. There's NO WAY Ferris could realistically run 'out of sight' faster than the mom can look up.
Jeanie's behaviour and decisions make NO SENSE whatsoever, especially singer Ferris LINGERS around a long time for the whole 'squinting' stuff, which also makes no sense.
It's of course preposterous that the dad never sees Ferris, although he's like 1 m from him SEVERAL TIMES during the day, and can see him 'jogging' next to his car directly, but that's a topic for another post about things that make no sense in this movie.
In any case, Jeanie makes no sense in this scene, either.