Near the beginning of the film, we see the girls running past a poster of _Creature from the Black Lagoon_ (1954) in 1952. It could be an advance poster, but this seems highly unlikely since "Creature" wasn't released until March 1954 in the States - let alone New Zealand.
The Doris Day LP record titled "Bright and Shiny" that the young lodger, Steve, has just bought and shows the family was recorded in 1961. (Also, 33 1/3 rpm LPs were not released until 1948. In 1953 when the film is set, long playing records were 12 inch).
When Juliet drops the gem, Pauline then points it out and we see a shot of it. Then we see a second shot of it, as Honora picks it up. Between the two shots the position of leaves and twigs around the gem changes.
In art class, Mrs. Collins picks up some papers and a wooden tray with a circular shape carved into one end of it, then turns and talks to Juliet. In one shot the carving is facing her. In the next shot, the carving is facing away from her.
Honora, Juliet and Pauline walk up from the bus terminus near Victoria Park, and Honora elects to have a cup of tea before going into the park. When they pass the entrance to the park, the camera follows them as they turn to enter the Victoria Park Tea Rooms, to their right. As they start up the stairs to the tea rooms, they pass a small sign on the ground advertising ice cream. In an earlier shot, at the close of the Prologue, Mrs Ritchie runs down the steps leading to the Tea Rooms. When she reaches the bottom of the steps, the ice cream sign is gone.
When Honora brings Pauline a tray of breakfast into her room, she gives Pauline the tray, then talks to her for a while. A crew member's face is clearly reflected in the window. Afterward, two hands holding the long pole of a boom mic are reflected in the window.
In art class, Mrs. Collins says "...and decide who wants to model and who wants to draw." In a wide shot of the class, the long pole of a boom mic being slowly lowered is clearly reflected in the windows on the right side of the room.
When Pauline, Juliet, and Honora are riding in the bus, they are clearly on the upper part of Dyer's Pass Road approaching Sign of the Kiwi, which means they have gone past their destination of Victoria Park.
Spoilers: Neither Juliet Hulme nor Honorah Parker have ever said they had a lesbian relationship. Hulme says they had an "obsessive friendship". The parents and adults of the time claimed this. Despite this, the film includes a graphic sex scene between characters who would have been 15 and 16 at the time respectively.
On the day Juliet coughs up blood in class, the date written on the chalkboard is 11 May. Although in real life, Pauline's diary notes that 11 May was the first day Juliet coughed up blood, this event occurred during the May holidays when the girls' school was closed.
Pauline's diary shows January 1st, 1954 as a Thursday, when it was really a Friday. Earlier in the film, a similar shot of the same diary clearly shows the previous year and date (Thursday, January 1st, 1953.)
The goof item below may give away important plot points.
Pauline and Juliet Strip off some of their clothes while singing "The Donkey Serenade" in the woods. In one shot after Juliet has been reduced to her bra, Pauline begins to remove her vest as she runs from the left to right of the screen. In the next shot the vest is back on.