There's been a slight improvement in the overall performance of charter schools since the center's 2009 report on schools in 16 states. Utah was not part of the 2009 study, but it was included in a new analysis of test scores.
Nationally, charter school students gain the equivalent of seven days of learning in reading over their traditional public school counterparts, and in math, charter students improved to the point where there was no difference in test scores.
"In general, we've seen progress in the charter school sector, slow and steady," Davis said.
Charters are public schools but have more leeway in how they hire staff or design curriculum. Nearly 9 percent of all K-12 Utah students attend a charter school. Enrollment has shot up from 1,526 students in 2002 to a peak of 50,785 youngsters in the 2012-13 school year.
The study did not rank the 26 states, but used test scores to gauge the amount of learning during the school year, Davis said.
Black students, students in poverty and English-language learners benefit the most from attending charter schools, according to the CREDO study. However, white and Asian students do not benefit, and in some cases actually lose days of learning.
Researchers were unsure why some states showed steady improvement with charter schools, while other states, such as Arizona, Nevada, and Utah, did not perform as well.
Last month, Utah's Charter School Board unveiled its plan to evaluate Utah's 81 charter schools in three key areas academics, finances and governance creating a baseline for comparing the schools next year. Charter board staff, along with CREDO, developed the new performance standards, which will be used to find best practices, warn of schools in trouble and monitor the overall system.
Chris Bleak of the Utah Association of Public Charter Schools hasn't looked closely at the CREDO study, said charter parents look at individual schools, not averages.
"There are charter schools performing at a high clip and others that aren't," Bleak said. "It's always valuable to measure schools and see how they're doing. We should hold all schools accountable."
Read the report
O See the new analysis on the website of Stanford's Center for Research on Education Outcomes. > credo.stanford.edu