When Cochise gets into the stolen car in front of Martha's, he has on sneakers; after they crash the car and he and Preach are running, he has on dress shoes.
After the guys steal potato chips and marshmallows at the zoo, they can be seen running without them, but in the next scene with the gorilla, they have the snacks again.
Early on, the gang hangs on to the back of a bus getting a free ride. When they first get on, it can be seen that the bus has no rear bench seat right on the other side of the rear window. Then, there is a rear bench seat with four people sitting on it, a young couple, and a woman with a little boy. Two shots later, the little boy is gone.
On Richard Morris' letter of acceptance from Grambling, his address is listed as 2716 East Superior Street, which would put his home about four miles out into Lake Michigan. Superior Street only goes as far east as the lake which is about 400 East.
The Chicago police car in the chase scene is a mid-size 1965 Plymouth Belvedere II. Assuming the film takes place in late 1964, a '65 model car could be correct, except the Chicago Police Department stopped using Belvederes after the 1964 model year, switching to the full-size 1965 Plymouth Fury I.
At the party, when Preach talks to Brenda, it is clear that the door opens from the outside. However, when Cochise throws Damon into that same door and breaks it, the door falls through. If the door opens from the outside, then there would be no way the door could fall.
Many automobiles from the 1970s are seen in many places.
A March 1974 copy of Mad Magazine (with the "Heads-You Lose!" back cover visible) is confiscated in a classroom.
Although many cars in the film show an attempt to conform to the era of the story, the city buses featured are right out of the '70s (when the film was made), along with some of the slang, hairdos, and urban apparel.
The film takes place in 1964, but there are Afro hairdos and people giving the Black Power sign and saying "right on". Those things didn't happen until about 1968.
In the opening montage, Chicago buildings such as Lake Point Tower (1968), the John Hancock Building (1969), First National Plaza (1969), the CNA Center (1972), the Standard Oil Building (1973), the IBM Building (1973), Sears Tower (1974) and Harbor Point (1975) are seen, none of which existed in 1964.
At the quarter party when Cochise is stopped by Johnny Mae, his voice is out of sync when he says, "Johnny Mae, how you doing?"
The boys jump on the bus at Lincoln Park Zoo, but they jump off at Lawrence and Kimball. No single bus runs between those two places.
The characters are at the Roberts Lounge, which is located on the South Side, but they all live on the West Side.