(Editor’s note: This commentary originally appeared in The Detroit News on Jan. 31, 2013.)

A new study by researchers at Stanford University shows superb positive effects for students attending charter schools in Michigan. It is the most rigorous study of charter schools ever done in this state and positions Michigan as one of the nation's leaders in charter school policy and performance.

No other study of Michigan's charter schools comes close to matching the sophistication or comprehensiveness used by Stanford's Center for Research on Education Outcomes (CREDO). This study compared students in charters to their peers in local public schools who were identical in terms of race, gender, socioeconomic status, prior academic achievement and more.

Researchers measured annual learning gains for about 85,000 charter school students over a five-year period and compared them to their "virtual twins" in conventional schools.

The findings were almost wholly positive for charter school students, and most impressive in Detroit. The typical charter school student made gains worth about two months of learning in reading and math. For a charter school student in Detroit, it was more than three months. Forty-two percent of charters outperformed conventional public schools in math and 35 percent did the same in reading. In Detroit, those numbers are 49 and 47 percent, respectively.

CREDO has evaluated charter school performance in 19 states using this same methodology. Of those, only Louisiana and New Jersey can hold a candle to Michigan. Louisiana charter school students also demonstrated learning gains of about two months when compared to their peers. In New Jersey, the average student in a charter made gains of about two months in reading and about three months in math.

Michigan's results were more consistent, though. Unlike Louisiana, students in Michigan charters demonstrated increased learning gains the longer they were enrolled. And while the New Jersey study found positive results for 44 of 54 of subgroups of student and schools, CREDO found a charter school advantage in 52 of 56 cases studied in Michigan.

What accounts for Michigan's success is hard to pinpoint, but certainly the state's charter school law and policies have a lot to do with it. In fact, a just-released analysis of such policies by the Center for Education Reform gave Michigan's policies one of only four "A's," ranking it fourth overall in the country.

Michigan is unique in the number of charter school authorizers it allows — such as public universities and community colleges — and the amount of autonomy it grants these authorizers.

These authorizers are not concerned with protecting existing K-12 institutions, which comes at the expense of denying quality charter school options for parents.

Michigan has historically allowed more charter schools than other states. The new CREDO study suggests that Michigan has a "highly dynamic market … creating a new positive stock of charter schools."

In time, the cap on charter schools will sunset. More net-positive competition will occur.

The typical Michigan student is better off for having enrolled in a charter school. Expanding school choice options in this state seems prudent.

Neither this recommendation, nor CREDO's findings, is a condemnation of conventional public schools. They are rather merely an affirmation that Michigan's 20-year-old charter school experiment is working and a compliment to the policymakers responsible for creating charter school laws and to the work of charter school authorizers, boards, principals and teachers.

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Michael Van Beek is the education policy director at the Mackinac Center for Public Policy, a research and educational institute headquartered in Midland, Mich. Permission to reprint in whole or in part is hereby granted, provided that the author and the Center are properly cited.