For centuries people weren’t sure how a child learned to speak. During all that time all children learned to speak a lot of different languages: English, Spanish, Chinese, Arabic and more. Some people thought that learning to talk was a miracle. Researchers at Harvard and M.I.T. devoted their lives to figuring out how children learned to speak. In 1995 two researchers from Kansas, Betty Hart and Todd Risley published Meaningful Differences in the Lives of American Children, which explained their research findings. It turns out that, before the age of three, some children hear millions of words more than other children, not different words, just words that all adults use every day.