A wide-eyed Lance Spencer, 12, stood against the wall, between a stone block once used to auction slaves and a glass-boxed gallery where a worker was adjusting the lights on a shawl that belonged to abolitionist Harriet Tubman.

“It’s cool!” the seventh-grader at Eliot-Hine Middle School in Washington, D.C., exclaims. “That’s what I think is interesting so far. … I wanted to see our history. I’ve learned so much, but there’s more that I want to know.”

Lance, two classmates and his broadcast-media teacher, Mandrell Birks, were threading their way through a nearly impassable gallery choked with reporters, curators and construction workers as the National Museum of African American History and Culture offered a preview of its collection.