Sandy Morton said she was upset when her 14-year-old son checked out two books from Hill Middle School's Library in Denver, KDVR-TV, Denver reported Wednesday.
"I was very upset," said Morton, whose son brought home "The Gun," by Paul Langan, and "One Fine Day, You're Going to Die," by Gail Bowen.
Both books are designed for reluctant teen readers, typically described as troubled students who don't like to read, and have plots about upset teens who threaten to kill their peers.
"It was unsettling to know that he could bring something like that home from school," Morton said.
The school said it removed the books and apologized to Morton.
A Denver Public Schools official said the books were designed for high school students and not middle school students.