The Substitute (2007)

A sixth grade class gets a substitute teacher who is unlike any teacher they've ever had before.  She mocks and insults them, seems to read their minds, and intimidates them.  After numerous complaints from the children, their parents demand a meeting with her.  But Ms. Harms is quite charming and the parents end the meeting by asking their horrid children to apologize to their substitute for lying about her.

The kids know she's not what she portrayed to their parents.  So they band together to figure out what is really going on.  They discover her house is dark, creepy, and empty except for a room full of chickens.  Convinced she is an alien or monster, the kids realize she has some evil plans for them, and they are on their own since their parents won't believe them.

This is a decent effort, but the ending wasn't really satisfactory.  It was made in Denmark so there is a different feel to the story than if it'd been done in the US.