In a report released Tuesday, researchers from Stanford University took on a question that Washington’s state auditors could not: What kind of academic impact do the state’s charter schools have on their students? Their answer, after studying three school years’ worth of data: Overall, charter-school students’ scores on state math and reading exams grew at a similar pace compared to their peers enrolled in traditional public schools. That finding was true for almost all student racial and demographic groups, with English learners being the notable exception.