Denver “Portfolio” Report’s Flaws Remain, NEPC Reviewer Confirms

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Key New Review Takeaway: Author response fails to address limitations in data and other problems.

A May report from the Progressive Policy Institute highlights multiple trends and reforms adopted in Denver between 2005 and 2014, most notably a “portfolio strategy” that includes a mix of traditional, charter, and hybrid public schools. The report argues that school autonomy via charter schools has improved student outcomes across the city and serves as a model for other cities.

Terrenda White, an assistant professor at the University of Colorado Boulder, reviewed the report, A 21st Century School System in the Mile High City, and criticized it for making causal claims to the effect that the author’s preferred Denver policies must have caused observed test-score gains and should therefore be emulated in other school districts. Professor White explained in her review that the data presented in the report were largely descriptive and did not control for the potential effects of multiple variables, thus posing insurmountable threats to the validity of any causal inferences. She also stressed that the district’s widening achievement gap, acknowledged in the report itself, should have given the author greater pause before proclaiming success and advocating emulation.

The report’s author responded to the review on July 28, 2016, and Professor White has now offered a rejoinder, engaging with that response and addressing each of the author’s two primary concerns. Though valuing the author’s effort to highlight markers of academic improvement among students, she maintains that the response does not address the important limitations of the data.

“The NEPC strongly welcomes these exchanges,” said Professor Kevin Welner, NEPC’s director. “A reader of the report plus the review and the continued exchange will understand the report’s strengths and weaknesses to a much greater extent than if the reader read the report alone.”

Find Terrenda White’s original review and her follow-up rejoinder at:

Find A 21st Century School System in the Mile-High City, by David Osborne, published by Progressive Policy Institute, at:

Find David Osborne’s response to the original review at:

The National Education Policy Center (NEPC) Think Twice Think Tank Review Project ( provides the public, policymakers, and the press with timely, academically sound reviews of selected publications. The project is made possible in part by support provided by the Great Lakes Center for Education Research and Practice:

The National Education Policy Center (NEPC), housed at the University of Colorado Boulder School of Education, produces and disseminates high-quality, peer-reviewed research to inform education policy discussions. Visit us at:

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William J. Mathis

Terrenda White
University of Colorado Boulder
(303) 492-0819
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