Continuity mistake: In the scene where Ferris is singing "Twist and Shout," you can see a building sign that reads '33 North Dearborn Street.' After the shot cuts, you can see an intersection of two streets: Adams Street and Dearborn Street. The address '33 North Dearborn Street' is a few blocks away from the intersection.
Continuity mistake: When Rooney gets on the school bus, he crosses a grass boulevard with no sidewalk to board it. The bus never moves. When the bus pulls away, there is a sidewalk next to the bus where the grass was.
Continuity mistake: In the scene where Ferris catches the foul ball, the television shows the stands where Ferris & company are sitting (down the left field line) as being in the shade. When the television shows the close-up of Ferris catching the ball, he is in the sun. When they have the actual shot in Wrigley Field, it is overcast.
Continuity mistake: Whilst Jeanie and the guy in the police station are talking, a man in a suit walks behind them and then takes a file from the woman at the desk. However, without walking behind either of them, he ends up on the other side of the room.
Continuity mistake: When Jeanie says 'I don't know why I'm here', there's no one behind her. However, in the next shot of her, about a second an a half later, there are three people behind her.
Continuity mistake: Near the very end, Ferris races home in vain as both Jeanie and his parents beat him home. Ferris is still in the kitchen as we see his parents at the base of the stairs, saying 'Let's go check on him.' They turn and start up the stairs. The next shot shows Ferris racing up the stairs. Next, we see the parents begin to mount the staircase (this time from a different angle) for a second time.
Continuity mistake: When Ferris Cameron and Sloane are driving into Chicago they're speeding and flying by every car, but in one shot you can see a car pass the Ferrari in the background. It happens soon after they go airborne and you can hear the Ferrari's engine roaring as the other car passes them by.
Continuity mistake: In the opening scene where Ferris is seen lying in bed he is facing his bedroom door. His mother moves him onto his back. When his sister comes into the room, there is one shot of him magically on his side again. In the next shot when he says, "Jeanie!" he has returned to his back almost instantly.