Americans are among the most mobile of people, with about one-fifth moving each year. But while mobility can improve the efficiency of labor markets, it seems particularly high among the poor and disadvantaged. The effect on children can be particularly devastating, according to a recent General Accounting Office study.

The GAO reports that an astonishing 30% of U.S. third-graders from families with annual incomes below $10,000 have changed schools at least three times since entering first grade--as have 25% of third-graders in inner-city schools. That's two and three times the rate among children who attend suburban and rural schools or come from more affluent families.

Such mobility exacerbates the problems faced by disadvantaged children. Among all income groups, frequent school-changers are more likely to perform poorly in reading and math, to repeat a grade, and to have health problems than children who have never changed schools. And, notes the GAO, mobile families and their children are among the least likely to take advantage of government programs aimed at improving educational success.

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