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Selection Bias in Charter School Success

It seems that the debate about the success of charter schools will never cease. A new UC Berkeley study claims to break new ground by finding that students who enter charter schools in the Los Angeles Unified School District are already higher achievers than those entering traditional public schools in the district ("Both traditional and charter schools in L.A. Unified could learn from this study," Los Angeles Times, Dec. 31).

I always try to keep an open mind when allegedly new evidence appears. But I was disappointed after reading about the study. Most students who enter any school other than the neighborhood traditional public school tend to be higher achievers. Why wouldn't they be? The fact that their parents have taken the time to investigate their choices is evidence that they are involved in their own children's education. Study after study has shown that parental involvement is absolutely crucial to achievement.  

Unless the Berkeley study controlled for selection bias, it is not nearly as informative as claimed. That's unfortunate because it found that students in charter elementary schools posted slightly greater academic growth than those in traditional public elementary schools, far greater gains in middle school, but not at all better gains in high school. These differences, if valid, need to be investigated further.

Why would the gains be so much greater in middle school than in elementary school? I would think just the opposite because elementary children are so much more malleable. Although the Berkeley study looked at charter schools only in the LAUSD, I would expect that further studies looking at charter schools in other districts would post similar results.

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