While YouTube EDU has been available for years (http://www.youtube.com/education), YouTube has now created a better way for schools to use the educational videos on YouTube without having to block the entire site.
YouTube for Schools allows schools to customize the content available in their school. All schools get access to all of the YouTube EDU content, but teachers and administrators can also create playlists of videos that will be available at their school. Students can only watch YouTube EDU videos and videos their school has added. [http://www.youtube.com/schools]
Check out YouTube for Teachers for teaching ideas and playlists of educational videos. [http://www.youtube.com/teachers]