School Choice or Best Systems_ What Improves Education_ - Margaret C. Wang [13]
These studies are unlikely to be reliable because they are both based on small samples of charter schools that were unmatched and not comparable to nearby traditional schools. The National Assessment surveys only about 3 percent of all schools, and charter schools are only a small percentage of this already small sample. Such small samples, moreover, are not designed to compare achievement of choice schools with that of traditional public schools and are likely to be misleading.
Reviews of Research
Hoxby’s national charter school study is one of 44 studies of U.S. charter school achievement included in Bryan Hassel’s review of the literature, the most comprehensive such review to date.17 Hassel aptly cautions against causal inferences about charter school effectiveness from single-point-in-time studies and bases his conclusions largely on studies that trace changes in individual students’ performance over time. Since students’ achievement in school is substantially affected by nonschool factors, differences among students at a single point in time should not be attributed completely or even substantially to their present schools. That would be analogous to comparing the completion times of runners who started at different locations.
Nor can preexisting differences among students be validly adjusted away by questionnaire indicators of such things as enduring family socioeconomic status based on student impressions of the parents’ income, occupation, and education, particularly among younger children and those who have undergone changing family circumstances such as a job loss or the death of a parent. Federal Title 1 poverty status (used to assign subsidized federally sponsored lunches) divides children into poor and nonpoor groups, but this dichotomy lacks precision and may also vary across youngsters’ lives. Some families, moreover, don’t report their incomes to school authorities since it might stigmatize them or because they think it is a private matter. For such reasons, Hassel singled out the 26 most rigorous causal studies, those that followed students and schools over time to measure their comparative progress. Of these 26 rigorous studies, he found that
• 12 concluded that overall gains in charter schools were larger than those in other public schools;
• 4 concluded that charter schools’ gains were higher in certain significant categories of schools, such as elementary schools, high schools, or schools serving at-risk students;
• 6 concluded that there were comparable gains in charter and traditional public schools; and
• 4 concluded that charter schools’ overall gains lagged behind.
Thus, in 16 of the 26 rigorous studies, charter schools excelled traditional public schools.
Seven studies that Hassel reviewed examined whether charter schools improve their performance over time, since new schools usually face start-up challenges such as educating and evaluating new staff and developing and evaluating curricula. Five of the seven studies concluded that they do. Since most charter schools in the nation are relatively new, their performance in the coming years can be expected to improve and further outpace that of traditional public schools.
Three Exemplary Over-Time Studies
Three longitudinal studies (those that measure changes in an attribute over time) provide examples of more rigorous research and yield particular insights on the effects of charter schools.18 Greene, Forster, and Winters provide