Continuity mistake: Mr. Moor is eating a sandwich when talking to Arvid. The size of the sandwich he is holding changes a couple of times from almost gone to a bite or two gone.
Charliegate - S1-E3
Continuity mistake: Dennis writes "who cares" on the chalkboard. The placement of the letters changes, most noticeably the S.
Continuity mistake: When Janice gets mad at the class when they don't believe she has a poltergeist, she puts her books and a pencil on the desk. The pencil is seen rolling off the desk, the next shot the pencil is back on the desk. At the end of the scene the pencil is back on the floor.
Continuity mistake: When Mr. Moore writes his name on the chalk board he underlines it. The line moves a few times throughout the scene.