New York City’s charter schools are making strides in closing achievement gaps between disadvantaged inner-city students and their better-off suburban counterparts, a new study concludes.
The study, conducted by Stanford University researcher Caroline M. Hoxby and her co-authors Sonali Mararka and Jenny Kang, is based on eight years of data for students applying to the city’s growing number of charter schools. It finds, for instance, that attending a charter school from kindergarten to 8th grade can close the achievement gap with a similar student in the affluent suburb of Scarsdale, N.Y., by 86 percent in mathematics and 66 percent in reading. By comparison, the “Harlem-Scarsdale” gap only widens over the same span of grades for students who remain in regular public schools, according to the study.
For high school students, the study also found, attending a charter school increased the likelihood that a student would earn a state Regents diploma by age 20 by 7 percent for each year spent in that school.
Charter schools, which are public schools allowed to operate largely independent of many traditional school district rules, are a major focus of the Obama administration’s education plans. Federal education officials have made it clear, in fact, that states deemed unfriendly to charter schools will be last in line for economic-stimulus funds from the $4 billion Race to the Top program. (“Obama Team’s Advocacy Boosts Charter Momentum,” June 17, 2009.)
Studies comparing student achievement in charter schools with that in regular public schools are difficult to do credibly, however, because students who apply and their families are presumably more motivated to succeed in school than those who remain in regular schools.
Ms. Hoxby was able to overcome that problem in New York City because its charter schools are oversubscribed, requiring administrators to use lotteries to allocate seats. According to Ms. Hoxby’s report, 94 percent of the students in the city’s charter schools got there by lottery.
That allowed researchers to compare students randomly assigned to charters with students who applied but did not win a seat in a charter school, thus providing for a more apples-to-apples comparison.
How Generalizable?
The promising findings contrast sharply with those from a widely reported national study published this past summer by the Center for Research on Education Outcomes, which is also based at Stanford. In that study, CREDO Director Margaret E. Raymond examined data for 2,403 charters schools in 15 states and the District of Columbia. She found that students in more than 80 percent of the charter schools performed the same as, or worse than, students in regular public schools on mathematics tests. (“Study Casts Doubt on Charter School Results,” June 15, 2009.)
“As with all studies of charter schools, you have to look at what you’re comparing,” said Ellen B. Goldring, a professor of education policy and leadership at the National Center on School Choice, at Vanderbilt University in Nashville, Tenn. Ms. Hoxby’s study was financed by the federal Institute of Education Sciences through the center.
“Clearly, the lottery method is the gold standard,” Ms. Goldring added, “but it is one locale and it is generalizable only to schools with oversubscribed lotteries.”
“The CREDO study is looking across states and using a matching method, so they’re just asking different questions,” she said.
Jeffrey Henig, a professor of political science and education at Teachers College, Columbia University, in New York, said the explanation for the differing results could be even simpler.
“It could just be that New York’s charter schools are better,” Mr. Henig said. “This is a pretty strong study design-wise,” he said of Ms. Hoxby’s study, “and it shows effects that, if aggregated over time, are substantial.”
But another possible explanation for the sharply contrasting results, said Ms. Hoxby, may be that the CREDO findings suffer from a “serious mathematical mistake.” The problem, she said in a separate analysis, is that Ms. Raymond compared the achievement of individual charter students with that of groups of students from nearby public schools, without making the statistical adjustments necessary to account for the natural downward biases that result from that sort of calculation.
Ms. Raymond, who was traveling most of yesterday, said in an e-mail message that she was reserving comment on Ms. Hoxby’s criticism. “Her comments deserve similar careful attention,” she wrote of Ms. Hoxby, “and we will reserve comment until we have had a full opportunity to consider her memorandum.”
Inside ‘The Black Box’
In her study, Ms. Hoxby found that, by the 3rd grade, the average charter school student was 5.3 points ahead of lottery “losers” on state exams in English and 5.8 points ahead in math. (That’s on test scales of 475 to 800 points.) After that, the charter school students gained an additional 2.4 to 3.6 points a year beyond the regular public school students who failed to win a charter spot in the lottery.
“When you see good results like that coming out of a city like New York, it just makes you realize what’s possible,” said Robin Lake, the associate director of the Center on Reinventing Public Education, at the University of Washington at Bothell. “Charter schooling can be an effective tool if done right.”
Ms. Hoxby said she calculated the Harlem-Scarsdale achievement gap—a 35- to 40-point spread—to give New Yorkers a concrete idea of what her statistical results mean.
“I think when people talk about the achievement gap it’s unclear what they’re referring to,” she said. “Sometimes it’s black and white, and sometimes it’s affluent and poor. If you say Scarsdale in New York, people know what that means.”
Experts said Ms. Hoxby’s study is also important because it “gets inside the black box,” attempting to explore what successful charter schools might be doing differently with their added autonomy. Schools that held classes 10 or more days longer each year tended to produce better student achievement, for example.
“I think one thing that really came out of the data very strongly is definitely this long school year,” Ms. Hoxby said. “These students start out well behind more-advantaged students, so having them spend longer time in school is a way to make up some of that advantage.”
Likewise, researchers found that the average charter school in the study stayed open eight hours a day, with some providing services for as long as 10 hours.
Other school characteristics associated with better student achievement included: more time spent on English instruction; teacher pay plans that were based on teachers’ effectiveness at improving student achievement, principals’ evaluations, or whether teachers took on additional duties, rather than traditional pay scales; an emphasis on academics in schools’ mission statements; and a classroom policy of punishing or rewarding the smallest of student infractions.
Practices that didn’t seem to affect student achievement, on the other hand, were class size, parent contracts, or the number of years schools were in operation, according to the report.
Ms. Hoxby cautioned, however, that the characteristics the study identified don’t necessarily cause higher achievement, but might provide some clues for further study.
“It could also be,” she added, “that these are part of a package of things that have a positive effect on students.”
