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A new report from Stanford University’s Center for Research on Education Outcomes, comparing the rate of learning in California charter schools against district peer schools, finds mixed results that are not nearly as impressive as the gains found in Los Angeles schools, the subject of a CREDO report released last week.

In the latest survey, CREDO found that, on average, charter students in California gain an additional 14 days of learning in reading over district school peers but lag behind by 14 days of learning in math.

Overall, the new results for charter students represent an increase of seven days of learning in both reading and math, compared with CREDO’s previous analysis of state charters in 2009.

“The results for the California state-wide report are varied,” Margaret Raymond, Director of CREDO, said in a press release. “While we see improvement in the results of charters, particularly for those students who attend charter schools in urban areas, overall the results continue to be mixed.”

The analysis represents data from 393,492 charter school students attending 994 charter schools, who were followed for as many years as data are available, CREDO said.

In another finding, students attending charter schools affiliated with a Charter Management Organization have better learning gains than district school peers in both reading and math. The positive impact is equivalent to about 36 additional days of learning in reading and 28 more days in math.

The report on LA schools found that a student in an urban LA charter gains 50 more days of learning in reading and 79 more days of learning in math, compared with a peer in a traditional district school. And a student gains about 65 more days in reading and 101 additional days in math.