Let's consider, for example, how the deadly and divisive Civil War and Vietnam War get treated in the classroom. They don't get ignored because that would be a glaring omission. But they aren't exactly "taught" either. They are propagandized and rationalized.
In a feature article for the Washington Post on the occasion of the sesquicentennial of the Civil War, reporter Nick Anderson told about how fourth graders in a school in Virginia, a state that had been embroiled in the war, built and floated models of two war ships to reenact the naval Battle of Hampton Roads.  Reenactments are a perfect tool of the establishment. They are entertaining and they teach children how to think and act militarily. Children are taught the obligatory rationale that abolition of slavery was the war's reason, with no mention of Lincoln's racism and imperialistic reasons for keeping the nation intact for future expansion.
Now let's move forward from the end of that war to the Vietnam War, one of the most senseless and shameful wars America ever waged. Few high school students apparently are told how joyous the Vietnam people were over regaining their independence once America left humiliated in defeat or that a string of five American presidents and their administrations lied about the reason for that war, starting with President Truman when America first supported France's attempt to retain colonial rule of Vietnam and then took over when France failed. America's corporate/militaristic state had no intention of letting Vietnam rule itself. Although there's passing mention of the revealing "Pentagon Papers" in high school textbooks, few if any apparently delve into those papers or quote Daniel Ellsberg's conclusion that, "It wasn't that we were on the wrong side; we were the wrong side." 
Even if a classroom textbook were more rather than less objective and comprehensive about America's history, teachers are not independent agents and must be careful what they teach from the textbook and beyond it. Teachers who question or criticize America's warring and spying risk losing their jobs and some have.  It is thus hardly surprising that most social studies teachers in America spend scant time on controversial issues such as America's wars and discourage students from talking or writing about them.  Administrators who fire teachers for what they teach have the backing of the U.S. Supreme Court, which has never ruled against America's warring and spying, and believes it's perfectly constitutional to muzzle teachers. 
By Actually Teaching Warring and Spying
Not for an instant would I think that that fourth grade teacher meant to teach her pupils elementary naval battle maneuvers to be remembered and perfected as they continue their education. That opportunity comes later in a variety of ways, and the war/spy complex doesn't miss any of them. One of the most blatant examples that I know about is the Air Force's "CyberPatriot" program to teach middle and high school students with the aim of recruiting them later for careers in cyber security.  I would call that "grooming future spies in the skies."
Then there's the case of Chicago's public school system, reportedly "the most militarized in the country, boasting five military academies, nearly three dozen smaller Junior Reserve Officer Training Corps programs within existing high schools, and numerous middle school Junior ROTC programs---nearly all located in low-income, minority neighborhoods."  The person apparently most responsible for this militarized education in the Windy city was its CEO of public schools who later became President Obama's Secretary of Education. This probably means that as Chicago goes so does the nation.
What could be considered as sort of an enlarged, walk-in classroom are museums that imbue impressionable young minds with the "patriotic" spirit of war. For example, "The Price of Freedom: Americans at War" is an ongoing exhibit at the National Museum of American History in the nation's capital. David Swanson, author of numerous anti-war books says "The exhibit is an extravaganza of lies and deceptions," but then adds that "---overwhelmingly the lying is done in this exhibit by omission. Bad past excuses for wars are ignored, the death and destruction is ignored or falsely reduced."