This year Constitution Day is celebrated on September 17, commemorating the signing in the U.S. Constitution on September 17, 1787. To celebrate this day, the National Archives have a number of activities to help teachers and students explore the Constitution. Teachers in particular may also be interested in the Library of Congress Constitution Day Resources page, with contains a number of educational activities, as well as links to primary resources. The Constitution Center will be broadcasting some of their most popular events live on their site.
Looking for more U.S. Constitution resources? The Detroit Area Library Network (DALNet) has put together an excellent collection of resources on the subject.