Why don't we have real data on charter schools? (They don;t want us to know they are not better.)

http://www.alternet.org/education/why-dont-we-have-real-data-charter-schools?akid=12328.294211.10cm4N&rd=1&src=newsletter1021859&t=15

Michelle Rhee, the former Washington, DC, schools chancellor (and ex-CEO of StudentsFirst, a market-based school-reform organization), seemingly agrees, stating that “accountability has to sit everywhere in the system. The children have to be held accountable for what they’re doing every day; the parents, teachers, school administrators, all the way up.” Education Secretary Arne Duncan, supportive of many charter-school initiatives, has spoken on how we “need to be willing to hold low-performing charters accountable.”
The problem here is that charter schools are frequently not accountable. Indeed, they are stunningly opaque, more black boxes than transparent laboratories for education. According to a 2013 study by the Center for Research on Educational Outcomes at Stanford University, only 29 percent of charter schools outperformed public schools with similar students in math, while 31 percent performed worse. Most charter schools, in fact, obtained results that were no better than traditional public schools. So what was that 29 percent doing right? And what went so wrong with the failing 31 percent? There are a few reasons why it’s nearly impossible to find out.
To begin with, unlike public schools, which are required by law to show how they use public resources, most charters lack financial transparency. Many of the most successful charter schools pay higher salaries to teachers and administrators and offer students a longer school day and year. A recent study of the highly acclaimed charter-school chain KIPP (Knowledge Is Power Program) found that “KIPP receives an estimated $6,500 more per pupil in revenues from public or private sources” compared to local school districts.

There is also anecdotal evidence that some charters find ways to remove children with academic or behavioral problems through punitive discipline and professional “advice” to parents about their child’s lack of “fit.” When this occurs, local public schools end up enrolling a disproportionate number of “high-need” children—and, not surprisingly, their performance statistics decline. A 2006 study conducted by the Parthenon Group, a private consulting firm, found that many of the schools labeled “failing” and targeted for closure by the state’s Department of Education enrolled a disproportionate number of challenging students.