Revealing mistake: During the first shot of Larry being pushed out of the car, it's blatantly a stunt double who is taller, thinner and has shorter hair than the actor.
Revealing mistake: When Nathan walks into the classroom singing, the center sliding glass door on the back bookcase is closed in the initial overhead long shot, but in the tracking shots that door has been pushed to the side, so as not to see the reflection of the camera/crew as Nathan walks up the aisle following the camera. (01:42:15)
Revealing mistake: In the parking lot of what is supposed to be Busch Stadium in St. Louis, Missouri, all the cars have Florida license plates. This happened because Ron Howard shot much of the film in Florida, not in St. Louis, Missouri.
Answer: If a child becomes estranged from their father after their parents have divorced, it's not all that uncommon for the child to take their mother's maiden surname instead of their father's.
raywest ★