Houston ISD says the teacher made a mistake. The movie was shown this week at Shearn Elementary on Houston's south side.
'Insidious' looks like a freaky movie, even for adults. Entertainment Weekly calls it a haunted-house movie that has some of the "most shivery and indelible images in any horror film in decades."
Rated PG-13, parents are "strongly cautioned" against their children watching it.
"I couldn't believe what he was telling me. From school -- he's in fifth grade," parent Mary Baker said.
So you can imagine Baker's horror when her 10-year-old son, Kyle, came home, saying he watched it at school.
"I think it was a very poor choice for a teacher that was educated. He knows better, and it affected my son horribly," Baker said.
Baker says a teacher at the school let her son's class -- a group of 10- and 11-year-olds -- choose between a funny and scary movie, and 'Insidious' was one of their options.
"He was physically sick," said Baker. "He was throwing up last night until almost midnight. Then got in my bed and ended up sleeping with me the rest of the night."
A spokesperson for HISD confirms the teacher showed the PG-13 movie in class without approval. They added that their policy is that "any film shown in class must be approved by the principal. As a result, the teacher will be reprimanded and an apology letter will be sent home to parents."
Other Shearn parents agree.
"Do you let your student watch horror films?" we asked parent Guadalupe Gil.
"No I don't," she said.
"So I wouldn't feel comfortable," parent Heather Mouton said.
The teacher made a mistake. Baker just hopes now he's learned his lesson.
"Kids are affected, they're affected. It affects them. The little things count - even movies," Baker said.