Continuity mistake: When Hagrid and Slughorn are drinking after Aragog's funeral, Slughorn's cup is considerably larger than Hagrid's (an effort to show size difference between Slughorn and Hagrid), and note when Slughorn holds his cup how large it is compared to his hand. But after Hagrid passes out Slughorn's cup is now the same size as Hagrid's cup - Slughorn's hand is resting on the table right beside the cup, which is now significantly smaller compared to Slughorn's hand. (01:50:05)
Continuity mistake: After Hagrid passes out in his hut, when Harry tells Slughorn of Lily's sacrifice the vegetables behind Harry change position on the shelves. (01:50:40)
Continuity mistake: On top of the Astronomy Tower, before Dumbledore and Harry leave to retrieve the locket, Dumbledore hair moves in front of his left shoulder in shots behind him. (01:57:35)
Continuity mistake: When Harry and Dumbledore return from the Horcrux cave, Dumbledore sits down with his arm around Harry's neck. When Dumbledore asks Harry to go fetch Snape, his arm suddenly disappears, and there was no time for him to have moved it. (02:10:00)
Continuity mistake: When Harry is kneeling beside Dumbledore's body, at the foot of the Astronomy Tower, Ginny joins Harry and holds him at his left side (viewer's right). In the last close-up of Professor Dumbledore's face, Harry is visible in the background with a space to his left and Ginny is now gone. That same angle was shown before Ginny joined Harry.
Continuity mistake: When Harry, Ron and Hermione are at the Three Broomsticks talking with Slughorn, Slughorn spills his butterbeer on Hermione and the table. Still in the conversation, the table is shown, but it's dry. Then a little later, there is foam on the table but only near Harry's glass. The rest of the table is still dry.
Continuity mistake: At the Three Broomsticks, when Slughorn spills the drink the foam by his fingers disappears, reappears, disappears, and so on.
Continuity mistake: When Slughorn and Harry are talking at The Three Broomsticks, Slughorn's grip on the silver mug repeatedly changes. His fingers are either at the top of the mug or at its center, depending on the camera angle.
Continuity mistake: In the living room at the Weasleys' house, while Harry, Arthur, Nymphadora and Lupin are talking, in the shot facing Lupin, Harry's shoelace is untied. After a brief cut to a shot facing Nymphadora and Arthur (where we can see Harry's hands), it cuts back to the original angle and now the shoelace is tied. (This has nothing to do with Ginny tying Harry's shoelace much later on.)
Continuity mistake: In the scene with Weasley's Wizarding Wheezes, as the camera pans up the front of the store, one sees the store name (in gold lettering). However, when Harry, Ron, and Hermione leave the store to follow Draco Malfoy the store name is no longer present.
Continuity mistake: Near the start, when Slughorn shows Harry the framed photographs, the frames change position between the wideshot and close-ups.
Continuity mistake: As Harry and Luna come through Hogwart's gates, an Auror standing outside begins to walk backwards in through the gate. He makes it half-way through, but in the next shot, he is still at the end of the gate.
Continuity mistake: In the Room of Requirement, when Draco first uncovers the Vanishing Cabinet, the items on the floor behind him change position between the overhead shot and next close-up.
Continuity mistake: After drinking the poison in Slughorn's office, Ron falls and in the overhead shots the top of his head is near the rug's edge, but in side shots his head is well below the large diamond pattern, more than a foot away from the edge.
Continuity mistake: When Harry finds Hermione crying at the bottom of the stairs, with the conjured canaries flying overhead, there are numerous leaves/debris on the lowest steps and near her feet, but in the shots looking down from the top of the stairs the area is clear. (This has nothing to do with the few leaves that blow about.)
Continuity mistake: In the Great Hall, when Ron sits down with Harry and Hermione before Quidditch, the newspaper Hermione is reading goes from her hand to under her arms, then back again, etc, between shots.
Continuity mistake: In the Great Hall before the Quidditch match, in the shots facing Hermione she is sitting opposite the empty place setting beside Ron, but in the shots facing Ron she is directly opposite him. Take note of the goblets, plate of eggs, etc.
Continuity mistake: In the scene before the Quidditch match, while Ron, Hermione and Ron are talking and Ron believes that Harry put something in his drink - in some angles Ginny is sitting directly next to Harry with their arms only an inch or two apart, in other angles Ginny's arm is nowhere to be seen, when they are sitting close enough that she should be visible.
Continuity mistake: At the Three Broomsticks, when Slughorn and Harry speak, Slughorn holds a silver mug with a high foam head, but in the shot facing Harry, before Slughorn actually spills the drink the mug's foam head is gone (visible at the bottom of the screen), only to reappear when he spills it on Hermione ,whereupon the same previous angle is shown again without the foam.
Continuity mistake: During the first potion class scene during the movie, Hermione and Lavender are seen standing next to each other while being taught potions by Professor Slughorn. However, within the first minute or so of the lesson, Hermione and Lavender are standing far apart, then in the next shot, they are standing close together, with what looks like barely any space to move. They remain like this for the rest of the scene, but you can see the gap between the two within the first few minutes of the class.
Answer: Leaving an untrained young wizard, who obviously has some behavioral issues and has no idea he is magical, alone in the Muggle world would be extremely dangerous. Dumbledore does not yet know that Riddle will become evil, but like any teacher, he wants to give a troubled youth an opportunity to find a new path in life.
raywest ★