Web filtering in schools

As computing has become ubiquitous in schools so has a need to protect students from inappropriate content across the web, while also allowing students to use content-rich educational sites that can enhance the learning experience. Rather than simply blocking off large portions of the Internet, many schools are utilizing customizable web filtering systems that provide them with greater control over which sites are allowed and which are blocked.
Content Filtering in The United States.
The Children's Internet Protection Act (CIPA) requires that U.S. schools have appropriate measures in place to protect students from obscene or harmful online content in order to be eligible for discounts on internet access or internal connections through the Schools and Libraries Program of the Universal Service Fund, commonly known as the E-Rate program. There are a number of commercially available free and paid services that allow schools to meet CIPA requirements and receive the discount.
Types of Filtering.
The FCC and CIPA do not specify how the filtering needs to be done, so most schools are using a combination of DNS, Browser and Firewall-based filtering.
DNS Filtering.
The DNS filtering happens at the domain resolution layer of the Internet and does not allow the IP address of an obscene or harmful website to be discovered. There are multiple paid products that perform such work, but many schools are leveraging free solutions to filter non-safe sites.
Browser Filtering.
Some Browser extensions allow parental control to be enabled to restrict non desirable websites categories. For CIPA, those categories include any website with adult-only content.
Firewall-based Filtering.
Firewall-based filtering can be done at the IP layer or using Web proxies to intercept and filter HTTP and HTTPS requests to websites that are not kid safe. This type of solution is difficult to implement as much of the web is moving to HTTPS, so it does not have a high efficiency.