Continuity mistake: When Flash is teaching "The 7 Laws of Crime," he writes "extortian" which is spelled incorrectly with an "a". Yet, when he says, "If you don't start using your noggins...," the word "extortion" is spelled properly with an "o", but then it reverts back to the incorrect spelling in following shots. (00:40:30 - 00:43:35)
Continuity mistake: When Miss Fritton boxes with her niece, Annabelle wallops her aunt, and as Miss Fritton falls backwards we see her shoeless foot fly up. However, when she's lying flat on her back she has both shoes on her feet. (00:42:45)
Continuity mistake: When Kelly writes "The Heist" as the 7th idea during Flash's class on "The 7 Laws of Crime," her handwriting on the board is completely different in following shots. (00:44:35)
Continuity mistake: On the school trip to the National Gallery, Kelly finds the paintings location on the far wall facing her, with marble trimmed doorways behind her within an open area, directly opposite the painting. The girls plan is based on this location. However, when Kelly, Taylor and Andrea reach the painting during the heist, entirely different walls with paintings are opposite the painting. (00:45:55 - 01:24:20)
Continuity mistake: When the girls give Annabelle all the makeovers, the first is 'odds', second is 'chavs' (with gold necklaces and side ponytail), third is 'posh totty', fourth is 'geeks', and before the fifth 'emo' makeover, Annabelle is made up like a chav once again. (01:03:15)
Other mistake: After Kelly and the twins climb out of the sewer tunnel and hear footsteps, the twins sit atop the steel grating pretending to cry while the rest hide below. All the walls and paintings behind the twins are the very same ones behind Kelly, Taylor and Andrea later, when they've finally reached their target painting, in a different area of the gallery. We can even see the square of wood planks covering the area of the steel grating seen earlier. (01:13:35 - 01:24:00)
Continuity mistake: When Kelly, Taylor and Andrea reach the balcony over the audience, there are two large paintings and a sculpture behind them. There are two large paintings on the balcony across from them as well. In the following shots the sculpture switches from male to female repeatedly, and the painting from the opposite balcony actually appears on the other side. For example, when Kelly whispers, "We need more cover," the sculpture is male, but when she climbs over the banister to the zip line, the sculpture is female. Also, when Miss Fritton swings across to rescue Kelly, the painting behind her is the same one that should be on the opposite balcony. (01:15:25)
Continuity mistake: After Kelly uses the crossbow, the line is wrapped around the banister, centered between the ten balusters. In following shots, its either at the right end of the banister, or just hanging over the banister, or wrapped at the center again. (01:16:10)
Deliberate mistake: As Kelly begins to make her way across the zip line over the audience, the overhead shot looking down at her is a flipped shot. Note that her watch is now on her right wrist, whereas in the previous and following shots its on her left wrist. (01:16:15)
Continuity mistake: During the grand final of School Challenge, in every overhead shot of the zip line, host Stephen Fry is seen below wearing the mortarboard, but in all shots facing him he is bare-headed. (01:17:20)
Deliberate mistake: After the heist, when Taylor and Andrea are told they have only three minutes to the end of the show, there is an overhead shot of them on the zip line that is flipped. Note that Cheltenham and St. Trinian's have switched sides and the letters on the prop books behind them are backwards. (01:27:45)
Factual error: During "School Challenge" the volume of a sphere is given as Pi R cubed. It should be four thirds Pi R cubed.
Continuity mistake: When Flash is writing Theft next to no.6 on the board, Blackmail has appeared next to no.5 - Flash couldn't have written it on the board previously because when we see the board (before Theft is written on it), there is a blank space next to no.5.
Revealing mistake: There is one shot where Andrea, whilst dancing to avoid the security beams guarding the picture, puts her leg through a beam but nothing happens.
Revealing mistake: When the girls are crawling along the wire, There is one shot where it looks projected.
Continuity mistake: When the girls are crawling back along the cable, there is a shot from just in front of Steven Fry which shows them behind him, when every other shot shows that the cable is over the audience.
Continuity mistake: When Flash and the girls are going through the 7 Laws of Crime, kidnapping is written on the board next to the no.4. When it comes back to the scene a little later, Kidnapping is no longer on the board.
Factual error: When the group from Cheltenham arrive to play hockey, the name is spelt wrong on the bus. It's spelt Chelteham.
Continuity mistake: When Colin Firth is tasting the vodka, he dips his index finger into the drink, but he tastes it with his middle finger.
Continuity mistake: Before the heist, when Kelly is pulling herself across the cable, the locking carabiner hanging from the line pulley flips over and turns itself upside down between shots, which is impossible to do with Kelly's weight hanging from it.
Chosen answer: She wasn't in one of the groups (Geeks, Emos, First Years, Posh Totties and Chavs), she was an outsider. The girls later give her a makeover as each one of the cliques, but she ended up as herself and said she "felt like a St Trinian".
Sierra1 ★