Race is central to the debate surrounding Trayvon Martin, the black Florida teen shot by neighborhood watch volunteer, George Zimmerman. Many media outlets first identified Zimmerman as "white," but his father describes him as a Spanish-speaking minority. Host Michel Martin explores the question, "who is white?" with sociologist Jean Halley.

Dennis Walcott oversees a school system with more than one million students. Graduation rates are below the national average, and studies suggest most of the city's high school graduates are not ready for college. But Chancellor Walcott tells host Michel Martin that, after one year on the job, New York City schools are on the mend.

Mitt Romney has taken the lead in voter support in Pennsylvania, according to a new poll from Public Policy Polling which shows the Republican frontrunner ahead of Rick Santorum, the former U.S. senator from the Keystone State, 42 percent to 37 percent. That lead was just on the 4.9 point margin of error, suggesting a tie. That's bad news for Santorum, however, as he dropped six percentage points while Romney gained 17 percent from a month ago.

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The number of people filing first-time claims for unemployment insurance stayed around a four-year low last week, the Employment and Training Administration just reported.

It says there were 357,000 such applications, down 6,000 from the previous week's revised figure of 363,000.

Claims have been running at the lowest rate since March and April 2008 for several weeks now.

Finding out that you have cancer greatly increases the risk of death by heart attack or suicide, according to a new study. That risk is especially big in the first week after getting the bad news.