Dr. Hoxby notes that we have long had data showing that students in private schools, whether using a voucher or paying their own tuition, do better academically than students of similar background in public schools. But what has remained unknown until recently was whether or not the student left in public schools are helped by the competition. Now Dr. Hoxby's results help answer this question with data:

My research shows that metropolitan areas with maximum interdistrict choice elicit consistently higher test scores than do areas with zero interdistrict choice. The 8th grade reading scores of students in highly competitive areas are 3.8 national percentile points higher than those of students in areas with no competition; their 10th grade math scores are 3.1 national percentile points higher; and their 12th grade reading scores are 5.8 national percentile points higher. Moreover, highly competitive districts spend 7.6 percent less than do districts with no competition. In other words, interdistrict competition appears to raise performance while lowering costs -- the result predicted by market enthusiasts. . . .

With strategies similar to those used to analyze the effects of interdistrict choice on public schools, I compared public school performance in areas where public schools face strong competition from private schools with public school performance in areas where little competition between public and private schools exists.

My comparison showed that all schools perform better in areas where there is vigorous competition among public and private schools. Areas with many low-cost private school choices score 2.7 national percentile points higher in 8th grade reading; 2.5 national percentile points higher in 8th grade math; 3.4 national percentile points higher in 12th grade reading; and 3,7 national percentile points higher in 12th grade math. In short, both traditional forms of choice -- choice among school districts and between public and private schools -- influence public schools in a positive manner. To place the influence of competition on school performance in perspective, if every school in the nation were to face a high level of competition both from other districts and from private schools, the productivity of America's schools, in terms of students' level of learning at a given level of spending, would be 28 percent higher than it is now. (p.71)

The results in Arizona were similar to those in Michigan and Milwaukee. . . . [Regular] public schools that faced charter school competition improved both their 4th grade reading scores and their fourth-grade math scores by 1.4 national percentile points a year. These improvements are above and beyond their achievement trends before charter competition. They are also larger than the improvements made over the same period by public schools that did not face charter competition.