First Lady Michelle Obama hosted a Black History Month celebration featuring Sweet Honey in the Rock, an award-winning female acapella ensemble, in the East Room of the White House on Wednesday for nearly 200 schoolchildren. Mrs. Obama seemed a bit surprised when the sixth- and seventh-graders from three local schools said yes, they knew slaves helped build the White House, that President Abraham Lincoln signed the Emancipation Proclamation upstairs in a bedroom named for him, and that the Rev. Martin Luther King Jr. and other civil rights leaders met in the building with Presidents John F. Kennedy and Lyndon B. Johnson to discuss the end of segregation. “So you guys know your history. That’s a good thing,” she said. “That means your parents and teachers are doing their jobs.” Mrs. Obama encouraged them to look beyond the names in the history books and to “think about the extraordinary people who live in your own world,” like parents, grand parents and teachers, “all those folks who play important roles in black history and American history every single day.” She said they will write history’s next chapter and they should work hard every day, always put their best foot forward, even when no one is looking, and support their families at home by making their beds, putting away dishes and cleaning their rooms. “That’s part of the preparation,” said Mrs. Obama, whose daughters, Malia and Sasha, sat in the front row with her mother, Marian Robinson. Before Mrs. Obama spoke, the students listened as retired Rear Adm. Stephen Rochon told his own story. In 2007, Rochon became the first black man to be named chief usher at the White House and director of the executive residence. President Barack Obama and the first lady have talked about opening up the White House and making it more accessible to the public. Wednesday’s event with Sweet Honey in the Rock was the first with a student audience, including some whose parents are members of the White House’s professional staff. The students attend Shaw and Stuart-Hobson middle schools, and KIPP DC: KEY Academy, a charter school.