After Silas and Jamal smoke in the the car, in one scene the car is filled with smoke, the very next scene, the air in the car is clear, it is also mentioned in the commentary track for that scene.
In the scene where I Need $$ steals Gerald's bike, when the truck has run over the bike and then backs up to run it over again, you can clearly see three bicycle wheels: two close together near most of the wreckage, and a third wheel a bit further back.
When Silas is waking Jamal up for crew practice, the alarm clock he holds near Jamal's face clearly reads 7:01AM. However, earlier in the movie, Bart stated that crew practice begins at 6:00AM. Jamal definitely would not have made it to practice.
In the scene where Jamal meets Silas, the toothbrush in Silas's hat alternates sides and faces in and out more than one time.
Baby Powder's vanity plate, "BPOWDER" is 7 characters. Massachusetts license plates have a maximum of 6 characters.
Silas and Jamal dig up the grave of president John Quincy Adams in an unspecified cemetery, when in reality, the president is actually buried in a family crypt beneath the United First Parish Church.
When the professor asks the students to identify the hanging plant, Silas says its a Neem Plant but its a String of Bananas (Senecio radicans).
When Jamal and Silas first pull in to take their THC tests and have their weed "mishaps," none of the audio matches their mouths as they frantically grab for their bud and blunts.