Jan Pinkava, who appears in the movie on the real television show Screen Test and won the Young Film-Maker's Competition of the Year Award, later went on to write and co-direct Ratatouille (2007) for Disney-Pixar.
Several instances of CG modification during post production are pointed out in the DVD commentary. At 1:17, 86:49, and 90:23 in the theater, both the SMOKING and NO SMOKING signs were added. At 43:48 where Lee Carter pinches the Guide Dogs for the Blind statue, "OPEN 5 DAYS A WEEK" was added on the store marque. At 57:29 the sign "Sixth Form Common Room" was added. At 58:00 the clock in the school clock tower showed the wrong time for the scene, so it was changed.
In the 6th form scene, director Garth Jennings mentions at 60:40 on the DVD commentary that for legal reasons they had to cut a bit showing a renowned 1980's toy (recalled because its paint contained lead) being licked on a dare by a boy. The end-piece for the bit, where the boy bursts out of a door and vomits, is still in the film at 62:49.
In the scene showing Will Proudfoot drawing in bed, director Garth Jennings mentions at 63:00 in the DVD commentary that his own humming was used in post production to replace Bill Milner's humming because the production had Bill hum "Tour de France" by Kraftwerk during the shoot but they were subsequently unable to clear the rights to use that song.
Between his audition and the start of the shoot, James Clarke's hair was cut off, which was a surprise to the production (11:00 in the DVD commentary). Rather than having him wear a wig, it was decided that his character, "Shaun", could be shorn.
Director Garth Jennings says that the round yellow sticker on the back seat of the bicycle Will Proudfoot rides to take Lee Carter home from school was used by the studio Props Department to designate that this prop was reserved for a shoot, but the film crew had neglected to remove it.
While the credits are rolling at 91:45 on the DVD commentary, Bill Milner says "My Mum's in there ... for "Underwater Costume Stand By" (referring to Deb Milner listed at 93:36), to which producer Nick Goldsmith responds "That's 'cuz I did the credits." There are no credits for the credits in the credits.
In the teachers lounge, the Scottish band are sitting at the table, dressed in the same costumes as the ones they wore in their music video for 'Driftwood', in which they also play teachers. Hammer & Tongs produced the video.