In many schools, student and staff discipline issues are handled in a unique way when it comes to Internet access. Rather than making rules and expecting people to be responsible and follow them, and punishing those who violate the rules-- when it comes to Internet access many school officials (counseled by network administrators) take the opposite approach. Rules are created and everyone is expected to violate them, therefore EVERYONE is punished by having access to broad categories of websites blocked (like blogs and wikis.) See the references to work by Scott McCleod for sources on this line of thinking.
Some school administrators cite CONTROL issues (directly or indirectly) as the reason web 2.0 sites are blocked. Reasons provided are sometimes that "students are off-task" on certain websites, students are "distracted" by certain websites, students "are playing games" on some websites, etc.
Classroom control and management are the responsibilities of classroom teachers and campus administrators, rather than IT staff members and network administrators. It is not and should not be the responsibility of IT administrators to "keep students on task" by blocking websites and entire categories of websites, like blogs and wikis. While students and others are legally prohibited from "disrupting the educational environment" via speech or actions (See the "Tinker Case" on WikiPedia for background) school officials are not legally bound to maintain classroom control or student "on-task behavior" by blocking websites or classes of websites.
Responsibility for providing meaningful learning tasks for students lies with teachers and administrators. Keeping students on task is not the job or role of the IT staff. Discipline issues and rules for online behavior should be handled the same as they are for non-online situations. Everyone should not be distrusted and punished with blanket policies which assume fault/wrongdoing.