This week, Harvard University professor Paul E. Peterson is addressing a Heritage Foundation audience to discuss his research on voucher students in various cities, including New York City. Peterson's message is likely to resemble the presentation that he and University of Wisconsin-Madison professor William G. Howell gave only a few weeks ago at a Brookings Institution symposium, reviewing a Peterson-Howell report on a three-year study of voucher students. The three-year study compared a "treatment" group (students who used a voucher to switch to a private school) with a "control" group (students who attended public schools).
In its findings, the Peterson research team reported that African-American voucher students consistently outscored those who remained in public schools. One newspaper trumpeted the Peterson-Howell research in an article headlined: "Scores of blacks rise with vouchers."4 But this upbeat coverage-and what is likely to be a similar spin by pro-voucher groups in the months ahead-is unjustified by the data, nor does it answer several questions raised by the data. In fact, Peterson and Howell specifically admitted that their three-year findings should not be used as an argument in favor of a "large-scale voucher program" serving all children in an urban school system.5 While voucher supporters are likely to focus on the three-year data showing gains for African-American voucher students, there are nagging concerns and questions about the Peterson-Howell data. For example, there were large fluctuations among subgroups and across the various years of the study, even in New York City. It is also worth noting that neither white nor Hispanic voucher students showed any academic gains over their public school peers. Additionally, a review of the New York City data reveals that reading scores actually declined for all groups of Hispanic voucher students, except for those in 7th grade. Peterson and Howell have made considerable effort to explain why black scores improved and why white and Hispanic scores did not-but to no avail.6 All of these considerations help to explain why Peterson and Howell concluded that there is "no overall private school impact of switching to a private school on student test scores …"7
Finally, this isn't the first time a Peterson-led voucher study yielded a host of questions or concerns. The conclusions drawn by Peterson from a voucher study released in August 2000 were seriously challenged. (The 2000 data were part of the overall three-year study that Peterson and Howell recently released.) Researchers Alex Molnar and Charles Achilles raised concerns about the August 2000 data, warning that the Peterson team's use of averaged results "may make the achievement impact reported appear more generalized than it is."8 And Mathematica Policy Research, one of the partners in the August 2000 study, was so disturbed by the conclusions drawn by the Peterson team that the firm took the extraordinary step of issuing a press statement entitled "Voucher Claims of Success Are Premature in New York City." Referring to the August 2000 data, Mathematica cautioned policymakers against "setting policy based on the overall modest impacts on test scores."9