What happens when a charter school opens within a school district’s boundaries? Does it hurt or help students overall? What about two charter schools in the same area—or 20?
These are some of the questions a newly released paper from a school choice research group seeks to answer.
The study from the National Center for Research on Education Access and Choice looks at the overall impact charter schools have on students’ academic achievement in both charter and traditional public schools in their area. This market-level view, which measures both charter schools’ effectiveness and how traditional public schools respond to the competition charters introduce, gives policymakers insights into when charter schools can improve student outcomes, and when they may not.
Much of the conversation around charter schools focuses on so-called participant effects—whether a student switching to a charter school learns more because of it, said Douglas Harris, an economics professor at Tulane University and the research center’s director. For this study, he wanted to look at how charter schools affect the overall education system.
“What we’re looking at here is a broader notion of charter effects that also includes all the spinoff effects and spillovers, like the competition with traditional public schools and the effects of charter schools on closing schools,” he said.
Previous research has found that charter schools can improve academic outcomes for students on average—both those who attend them and those who stay in local district schools. But that’s the average. For as many districts where charter schools improve outcomes, there are just as many where the opposite is true, Harris said.
There’s a lot of variability across the charter school sector, from the schools themselves to the kinds of students they serve to the types of policies that govern them, and the study found that their effects on student academic outcomes also vary widely.
That makes sense given that charter schools also open for a variety of different purposes beyond improving student test scores, said Alex Medler, the executive director of the National Network for District Authorizing, a group that supports school districts that oversee charter schools. Medler is also the vice president of the Boulder Valley school district board of directors in Colorado.
As an example, Medler points to his own district, where two charter schools use the Core Knowledge Sequence (a reading program that emphasizes building up students’ background knowledge)and are high-performing. Another is a Montessori school. But the rest of the charter schools in his district are alternative schools for students who have dropped out of school or are at risk of doing so.
“Those schools are going to underperform traditional high schools, but they could still be tremendously successful,” he said.
Given that, it’s not surprising the research found a wide range in efficacy, Medler said.
Under what circumstances do charters lift up performance for all?
So, what did the districts where charter schools led to improvements in student outcomes have in common?
The researchers identified 26 characteristics that have been associated with charter school effectiveness and analyzed data across 20 years from hundreds of districts. They found a few themes.
First, charter schools have the largest impact on student test scores in districts where students were already performing poorly.
The odds that a charter school will drive improvement in the overall school ecosystem are higher if schools and students are already low-performing. This may help explain why other research into charter schools finds that they are especially effective for students from marginalized backgrounds—because those students are more likely to attend low-performing schools.
Many state policies governing charter schools do not appear to affect whether they boost test scores districtwide. But there is one exception: school funding. In districts where school spending is higher across both charter and district schools, so too were the positive effects of charter schools on students’ academic achievement.
That’s likely because districts can’t respond to competition from charter schools unless they have the money to make improvements that will raise academic outcomes, such as hiring more teachers, Harris said.
Prior research suggests that public schools respond to the competitive pressure created by charter schools, Harris said. What the new analysis shows is their response “seems related to the amount of money that they have to spend.”
This finding is notable because some policymakers have elevated charter schools as a cost-saving measure because they tend to operate with less per-pupil funding than traditional public schools, Harris said.
“If we’re just viewing [charter schools] as a money-saving operation, that’s probably going to backfire because you still need money for these schools to work, too,” he said.
Finally, the researchers found that any positive effects charter schools bring tend to diminish as their numbers rise. It appears that when charter schools make up 50-60% of the market share, their positive effects on student academic outcomes fall to about zero.
While those estimates are imprecise because there are so few districts to study where charter schools account for such a high share of the student population, Harris said, they track with basic economics.
“When you have a monopolist, you just add one serious competitor, it changes the market quite a lot,” he said. Adding subsequent schools isn’t going to have the same impact as the first.
