Internet filtering in schools prevents students from accessing harmful or inappropriate Web content. But the filtering programs can sometimes leave harmful content unfiltered, but it can also block educationally relevant websites from students and teachers. Federal law requires some schools and libraries to filter and monitor Internet access, though the that law has been challenged in court.

Safety
The intent of Internet filtering in school is to provide a safe environment for students. Internet blocking in schools is usually thorough enough that it blocks most inappropriate content. This gives teachers confidence that students can use the Internet without encountering harmful content. Teachers can also do online research with the class and be confident that the research won't turn up inappropriate images.

Funding
The federal E-rate program provides discounted communication technologies to eligible schools and libraries. The Children's Internet Protection Act (CIPA), enacted in 2001, stipulates that schools and libraries must block or filter Internet images that may be harmful to minors. Schools regulated by CIPA must also adopt policies to monitor minors' activities online. Schools that do not follow these requirements cannot receive e-Rate assistance.

Access
A 2003 study by the Electronic Frontier Foundation and the Online Policy Group found that even schools that use minimal Internet blocking and filtering software block tens of thousands of websites without harmful content. The same study found that many websites related to state curriculum were also blocked. This over-blocking limits Internet access for students and teachers

Bias
CIPA outlines standards of what images it considers harmful to students, but Internet filtering software is not regulated by CIPA. The filtering software that many schools use is created by private companies that decide what kinds of content should be filtered. This leads to sites being blocked or filtered that do not fall under the criteria set by CIPA.

Litigation
Federally required Internet filtering has spawned litigation questioning the constitutionality of the CIPA requirements, including a lawsuit brought against the United States government by the Multnomah County Public Library in Oregon. A District Court found CIPA to violate the First Amendment, but that decision was overturned by the Supreme Court.