Twelve school districts sent letters to the state Board of Education by Monday's deadline, indicating their intentions to authorize charter schools. But don't expect any dramatic school turnarounds.

Studies have consistently shown that on average, charter schools do no better than traditional public schools at educating like students. In fact, the most credible large-scale study to analyze charter school performance—from Stanford University's Center for Research on Education Outcomes (CREDO)—found that 37 percent of charters actually performed worse than traditional public schools serving demographically like communities. Only 17 percent of charters performed better; the rest did about the same.

Still, backers insisted that Initiative 1240 was designed to learn from the experience in other states, and only replicate the best standards here. There are plenty of successful charter schools, advocates argued. For example, many of the 125 schools run by KIPP (Knowledge is Power Program).

So what is the secret of KIPP's success?

The true secret is more money, something public schools are starving to get. In 11 districts in the 2007 school year, KIPP received, on average, as much as $5,760 more per pupil than local school districts, according to a recent study. KIPP leverages this generous supplemental private funding in a straightforward way: giving students more time in schools while placing a reasonable limit on class sizes.

According to a 2012 Mathematica report, KIPP schools provided 192 days of school each year, nine hours a day. That's 45% more learning time than conventional schools provide — the equivalent of four added months of schooling.

We should not be surprised when four extra months results in several additional months of test-score growth.

If we truly wanted to learn from KIPP's example we'd start by amply funding our public schools, enabling them to provide the intensive wrap-around services that KIPP provides. But we don't. No, at comparable funding levels, charter schools are mostly an exercise in privatization and union-busting. I suppose for some, that's a worthy end in itself. But it sure as hell doesn't have anything to do with improving public education.