When her fourth-grade students entered her class last school year, 66 percent were scoring at or above grade level in reading. After a year in her class, only 44 percent scored at grade level, and none scored above. Her students performed worse than fourth-graders with similar incoming scores in other low-income D.C. schools. For decades, education researchers blamed kids and their home life for their failure to learn. Now, given the data coming out of classrooms like Mr. Taylor’s, those arguments are harder to take. Poverty matters enormously. But teachers all over the country are moving poor kids forward anyway, even as the class next door stagnates. “At the end of the day,” says Timothy Daly at the New Teacher Project, “it’s the mind-set that teachers need—a kind of relentless approach to the problem.”