It is true that there are many places on the internet inappropriate for students, but it's also true that many sites contain both inappropriate and useful content. Pages like Wikipedia and YouTube are great examples. I've seen instances where nbc, discovery, and other news and information based sites have advertisements which are inappropriate for students. A teacher can capture the essential content and show it to students offline, but students are eventually confronted with examples of the inappropriate material outside the school. Some sites should definitely be blocked, but I feel many schools err on the side of excess caution, removing beneficial tools. Eventually students will have the freedom to go anywhere on the internet. Maybe it would be better to let them encounter some "less" objectionable material in the controlled environment of school.