There were plans to produce a sequel, with the main characters on college spring break. Upon reading the script, Will Ferrell when promoting Semi-Pro (2008), said that he and Vince Vaughn had the same reaction when the story just felt like it was repeating itself.
In the scene where the gymnastics are taking place, when Vince Vaughn is doing the rings, you can see in the background it says "Harrison University - STATE CHAMPS". Because this is a college university, state champions would not be a possible achievement.
When Megan Huang is playing the tape of Dean Pritchard to
Mitch and Frank, the fraternity evaluation committee suddenly appears standing behind them towards the end when Dean Pritchard steals the tape.
What are the differences between the R-Rated version and the Unrated Version?
As many other sexual based comedies "Old School" needed to be trimmed to receive an R-Rating. 6 cuts running 79 seconds altogether are missing in said R-Rated version. A detailed comparison between both versions can be found here.