Obama spoke to students at Elizabeth Garrett Anderson School Thursday, her last day in Britain, where President Obama was attending the Group of 20 summit of industrialized nations, The Times of London reported Friday.
"If you want to know the reason why I am standing here, it's because of education," she told the 100 teenage girls. "I never cut class. I loved getting A's, I liked being smart. ... I thought being smart is cooler than anything in the world."
She urged the girls to believe their dreams, telling them they control their destiny.
"For nothing in my life ever would have predicted that I would be standing here as the first African-American first lady," she said. "I was not raised with wealth or resources or any social standing to speak of. I was raised on the South Side of Chicago -- that's the real part of Chicago."