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Recently, an evaluation of charter school performance compared to public schools by CREDO has been widely reported as showing charters significantly outperforming public schools in reading but comparable results in math.
Macke Raymond, founder and director of CREDO, characterized the results as “remarkable.” EdSource reported that “charter school students in California significantly outperformed similar students in nearby traditional public schools in reading.”
These claims are highly misleading. The report uses “significant” in its statistical sense of not by chance. Research studies involving large populations will almost always find statistical significance. Most articles about the report confused statistical significance with the common meaning of significance as “making a substantial difference.”
Statistical significance doesn’t tell you anything about the magnitude of the difference between populations which is usually reported as “effect size” in terms of standard deviation, which is a measure of how far the data spreads from the average.)
CREDO’s own data (see pages 38, 48 and 50) show that the difference between public schools and charters is minuscule. They report the difference in days of learning and explain that 5.8 days of learning equals 0.01 (one hundredth) standard deviation. So, the additional 11 days of learning found for California students in reading is equivalent to 0.02 standard deviations in reading and the additional four days equals less than 0.01 in math.
The research community usually suggests that a much larger standard deviations of 0.2 be considered a “small” effect size, 0.5 represent a “medium” effect size and 0.8 a “large” effect size. Most regard any effect size below 0.2 standard deviations as negligible even if statistically significant. The CREDO findings in reading for California are one-tenth of that 0.2 standard. Even the better growth results for Black and Hispanic students are one-fourth of that 0.2 floor.
Additionally, these results measured growth, or improvement in results, but even after growth, the performance of large numbers of charter (and traditional public school) students remain significantly behind.
There are scores of educational strategies and programs that are moderately (0.5 standard deviations) to highly effective (0.8+ standard deviations). These stellar educational efforts are between 20 to 40 times greater than what CREDO found.
The report and EdSource highlight some very effective charter schools run by charter management organizations. Organizations such as Aspire or schools such as High-Tech High do a fantastic job. But so do extremely effective traditional public schools. And there are six to nine times as many of those.
Given the similar distribution of the two groups, there are equal proportions of extremely effective schools in both populations. For example, according to statistical theory, there are 16% above one standard deviation above the mean. So, 16% of both charter and public school students are scoring one standard deviation above the mean—a “large” difference in statistical terms.
Yet because there are eight times as many students in California public schools as charters, there are many more students being served by high-performing public schools than are served by high-performing charters.
We should avoid the comparison rhetoric of charter versus traditional district schools. Instead, we should be applying what educators have learned from highly effective charter and noncharter public schools and how to remedy low-performing schools in both sectors.
There are proven strategies to do this:
- A quality curriculum, good instruction, and well-designed materials in reading, writing, math, history and civics, science, and the arts.
- A strong principal who builds teams and capacity to continually improve.
- An inclusive school climate focused on relationships.
- Community schools.
- Effective district support.
- Adequate financial support for schools.
These strategies are covered in detail in www.buildingbetterschools.com.
Since the charters and noncharter public schools essentially obtain similar results, a parent shifting to a charter on average will not move to a better-performing school as measured by test scores (only one aspect of school quality). However, there is considerable risk attached to charters that should be taken into account such as:
- The large percentage of charter schools that close (one-fourth within five years), many during the school year.
- The burden of attending a school that’s not close to home.
- The financial drain on the school district.
- Even after tightening accountability in California, the high levels of self-dealing such as public purchase of property which is kept or high salaries for founders.
- Too much time on test prep to the detriment of quality instruction.
So, let’s stop the comparison game and concentrate on learning from the best charters and public schools and remedying the dysfunctional schools in both sectors.
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Bill Honig is the former California superintendent of public instruction.
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