Continuity mistake: When Doug sits down to read his book, he has his book on his tray. This then disappears as the shot changes. (00:11:20)
Revealing mistake: When they first drive to their class, we see the street lights behind them. When Carrie pulls over to pick up Spence, she turns the steering wheel, but the lights in the back don't turn. (00:07:45)
Continuity mistake: In this episode, when Doug and Carrie are taking an adult literature class together, Doug comes down the stairs with his book in his hand, but when he sits on the couch he only has his book pillow and reading lamp, and runs back upstairs to get his book.
Visible crew/equipment: During the driving scene at 00:07:35 you can see a stage wall on the set to the right when the lights pass over the car. (00:07:35)
Continuity mistake: During both driving scenes, the street lights in the background do not fade away in the distance to indicate they are actually driving forward. When Doug, Carrie and Arthur are pulled over waiting for Spence (and again when waiting for Arthur at Dairy Queen), lights scroll over the car and the sound of a passing vehicle can be heard but no car is seen to pass by or drive away in the distance. (00:07:45)
Visible crew/equipment: When speaking to Doug about the book, a crew member is reflected in the window. (00:19:35)
Continuity mistake: In the first classroom scene there are two people sat to Doug's right. These people then vanish a few seconds later. (00:07:55)
Continuity mistake: When Doug falls off his chair his right arm is on the floor in one shot and on the desk part of the chair in the next. (00:09:10)
Answer: Sara hasn't been mentioned in later episodes, and it suggested in later episodes that she never existed, and that Carrie is an only child. Kevin James stated that the producers couldn't think of an good plots to use with Sara, so they left her out.