A middle school student in Missouri had trouble collecting images of people's eyes for an art project. An elementary schooler in the same district couldn't access a picture of record-breaking sprinter Florence Griffith Joyner to add to a writing assignment. A high school junior couldn't read analyses of the Greek classic "The Odyssey" for her language arts class. An eighth grader was blocked repeatedly while researching trans rights.

All of these students saw the same message in their web browsers as they tried to complete their work: "The site you have requested has been blocked because it does not comply with the filtering requirements as described by the Children's Internet Protection Act (CIPA) or Rockwood School District."

CIPA, a federal law passed in 2000, requires schools seeking subsidized internet access to keep students from seeing obscene or harmful images online—especially porn.

School districts all over the country, like Rockwood in the western suburbs of St. Louis, go much further, limiting not only what images students can see but what words they can read. Records obtained from 16 districts in 11 different states show just how broadly schools block content, forcing students to jump through hoops to complete assignments and keeping them from resources that could support their health and safety.