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Sunday, August 26, 2012

When does “Overall, no significant impacts are observed” mean rousing success? When talking about vouchers of course.

The Wall Street Journal has an odd article today trumpeting “A Generation of School Voucher Success” by voucher advocate Paul Peterson of Harvard and Matthew Chingos of the Brookings Institution.

The article is based on a study of a privately funded voucher program in New York City and its effects on college enrollments of those who received vouchers.

The study concluded that “Overall, no significant impacts are observed.”

However, there were statistically significant gains in the college enrollment rates of black students, and statistically insignificant gains for Hispanics.

Why the difference? It’s not clear, but consider what the study says about the two groups compared:

African American and Hispanic students differed from one another in a number of respects. Although students in the two ethnic groups had fairly similar baseline scores, African American students were more likely to be male, have a parent with a college education, come from one-child families (but are also more likely to come from families with four or more children), and, not surprisingly, come from a family in which English is spoken in the home.

But overall, the study produced “no significant impacts.”

If you read the study, check out p. 12, “Results,” which begins:

“The offer of a voucher is estimated to have increased college enrollment within three years of the student’s expected graduation from high school by 0.6 percentage points—a tiny, insignificant impact“

This somehow got spun in the WSJ article into “A generation of school voucher success!”

This study does not delve into test scores. One can only guess what the study would say if there were big test score gains.

The D.C. voucher program, the Cleveland voucher program and the Milwaukee voucher program have not produced any evidence of gains in test scores.

This is from the final evaluation of the DC Opportunity Scholarship Program:

There is no conclusive evidence that the OSP affected student achievement. On average, after at least four years students who were offered (or used) scholarships had reading and math test scores that were statistically similar to those who were not offered scholarships (figure ES-2). The same pattern of results holds for students who applied from schools in need of improvement (SINI), the group Congress designated as the highest priority for the Program. Although some other subgroups of students appeared to have higher levels of reading achievement if they were offered or used a scholarship, those findings could be due to chance. They should be interpreted with caution since the results were no longer significant after applying a statistical test to account for multiple comparisons of treatment and control group members across the subgroups.

Voucher students in DC saw no test score gains, but were more likely to graduate from high school:

The graduation rate based on parent-provided information was 82 percent for the treatment group compared to 70 percent for the control group.

Studies comparing voucher schools and public schools in Milwaukee and Cleveland have not detected any differences in test scores.

Earlier studies of the NYC private school voucher program showed no gains in test scores, which the study notes:

The original study of the New York City voucher experiment identified heterogeneous impacts. Although no overall impacts in reading and math achievement were detected, positive private-sector impacts were observed on the performance of African Americans, but not of Hispanic students (Howell and Peterson 2006, 146-52; Mayer et al. 2002, Table 20).

When vouchers are celebrated, the subject of test scores is irrelevant. When public schools are condemned, the subject is always test scores. Truly, a double standard.

Wonder why.

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