This week opens with a national observance of Constitution Day, designated by Congress and the president in 2004 as an occasion to commemorate the signing of the U.S. Constitution on Sept. 17, 1787 and learn more about our founding document. All public schools present programs about constitutional protections and the 39 men who signed it 225 years ago in Philadelphia.

Our Constitution, the world's longest surviving written government charter, remains a model for democracy advocates in the Middle East and other areas. Its first three words –– "We the People" –– affirm that the government exists to serve its citizens. Another source of strength is the balancing of powers among three independent branches of government: executive (president), legislative (Congress) and judicial (courts).

The Constitution and its 27 amendments also assure liberty, equality, majority rule, minority rights and state powers. Federal judges and ultimately the nine Supreme Court justices interpret the meaning of the Constitution and its amendments, which lets 18th century language apply in the Internet age. "The United States Constitution remains a vital and living document, strengthened by amendments, serving as both guide and protector of U.S. citizens and their elected officials," says a Constitution Day message from the U.S. Senate Historical Office. "It has survived civil war, economic depressions, assassinations, and even terrorist attacks to remain a source of wisdom and inspiration." The original parchment pages are at the National Archives in Washington, D.C.

Sponsor said: "Our ideals of freedom, set forth and realized in our Constitution, are our greatest export to the world." – Sen. Robert Byrd, D-West Virginia, who introduced the Constitutional Day bill six years before he died

Ex-teacher says: "Students deserve a more critical and nuanced exploration of the Constitution -- one that is alert to the race and class issues at the heart of our governing document." – Bill Bigelow, former high school social studies teacher in Portalnd, Ore., blogging Sept. 14 at Huffington Post

When you can vote: The 26th Amendment sets 18 as the national voting age. It was adopted in 1971 in response to student activism against the Vietnam War, when young men were drafted into the military