(Editor’s note: This is an edited version of a commentary that appeared in The Wall Street Journal on May 18, 2013.)

Public charter schools now serve 2.3 million children nationwide and enjoy growing bipartisan support. But they are still loathed by teachers unions and traditional public school officials more interested in protecting their piece of the school-funding pie than providing students trapped in failing schools a chance at a decent education.

Those familiar with the controversy over charters have probably heard of the 2009 study by Stanford University’s Center for Research on Education Outcomes. The CREDO study, routinely cited by groups opposed to school choice, analyzed charter schools in 16 states and found that, on average, only 17 percent were outperforming conventional public schools while 37 percent were doing worse.

However, CREDO noted that the study’s results “vary strongly by state and are shown to be influenced in significant ways by several characteristics of state charter school policies.” These include laws determining how many charters can operate in a state, who can authorize them and the level of autonomy these schools will have from certain state regulations.

Although largely ignored, this finding is especially relevant in light of a more recent CREDO study focusing solely on the performance of Michigan’s charter schools. The findings, released in January, portray Michigan’s charter schools as a clear-cut success story and provide lessons for other states.

CREDO found that 42 percent of Michigan’s charter schools are outperforming conventional public schools in math and 35 percent of charters are outperforming in reading. Only 6 percent of charters are underperforming in math and only 2 percent in reading. Further, 82 percent of charters produced growth in average reading test scores and 72 percent did so in math.

Of the 56 outcomes for different subgroups of students and schools the study dissected, 52 showed charter school students outperforming their peers in conventional public schools.

Perhaps the most notable finding was that from 2007 to 2011 the typical Michigan charter school student made annual academic gains in both reading and math equivalent to about two additional months of learning, compared with his or her peers in conventional public schools. The longer a student stayed in a charter school the greater the annual gains. After five years the average charter-school student made cumulative learning gains equivalent to an entire additional year of schooling.

As Cindy Schumacher, executive director of the Center for Charter Schools at Central Michigan University, told the press after the Credo report was released, the report “shows that the Michigan Model is working, with it leading to significant improvements for children, especially at-risk children who are historically underserved.”

The results were even more pronounced in Detroit, welcome news in a city where an estimated 47 percent of the adult population is functionally illiterate, according to the Detroit Regional Workforce Fund. The typical Detroit charter school student made annual gains worth about three additional months of learning in both reading and math compared with their peers in nearby conventional schools. Of the 100 or so charters in Detroit, 47 percent did significantly better than conventional schools in reading and 49 percent did significantly better in math. Only one charter school in Detroit did worse in reading compared with the city’s district-run schools.

The Michigan Education Association, the state’s largest teachers union, and other defenders of the public school status quo have tried to play down these results. Some point out that the Credo study didn’t include every charter school. In fact, the study included 86 percent of all charter-school students in the state and remains the most comprehensive and rigorous study of Michigan charter schools.

CREDO’s researchers matched about 85,000 charter school students to their “virtual twins” in local conventional public schools based on race, gender, socioeconomic status, prior test scores and other factors. Individual learning gains made by each set of students was then measured over time.

Sadly, the media have largely ignored CREDO’s findings or grossly distorted them. For example, days after the report was released Huffington Post ran a story calling it a “cautionary tale” and emphasizing that a large portion of charter schools’ average reading and math scores were below the state average. This comparison turns a blind eye to the well-documented impact poverty has on average standardized test scores. Since Michigan charters — often found in the school districts struggling most — enroll a far higher percentage of poor students (70 percent) than do the state’s conventional schools (43 percent), the finding biases the results against charters.

CREDO has analyzed charter-school performance in 19 states to date. Only Louisiana and New Jersey even come close to rivaling the results from Michigan. Why? Michigan allows a variety of public entities to authorize charter schools, the most common being universities and community colleges. This frees charter schools from needing school district approval to operate, which is like requiring new businesses to ask existing competitors for permission to open. By allowing more charters than most states, Michigan has developed a functional charter school market, so much so that lawmakers recently took the bold step of removing the charter school cap altogether.

Michigan’s charters also aren’t subject to teacher tenure laws and have the flexibility to retain or release teachers based on performance. This helps keep the best teachers where they belong, in the classroom, and the worst where they belong — looking for another line of work.

Finally, Michigan has several strong networks of education-management companies, including National Heritage Academies and New Urban Learning. These companies are much maligned for operating as for-profits, but as the CREDO study pointed out the charter schools they run did better on average than those directly managed by a charter school board.

It is no surprise then that the Center for Education Reform, a pro-charter nonprofit, recently gave Michigan one of only four “As” on its report card of state-charter school laws. If states want to create a healthy charter-school sector to boost outcomes for students, the Michigan experience offers valuable lessons.

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Michael Van Beek is director of education policy for the Mackinac Center for Public Policy, a research and educational institute based in Midland, Mich.