Not much. The National Alliance for Public Charter Schools has a new report out by Bryan Hassel which summarizes over 50-pages what the existing studies of charter schools tell us about student achievement. The report lists four key recommendations:

1. We need better research about how well students in charter schools are performing.

2. We need more and better research about why some charter schools perform so much better than other charter and non-charter schools.

3. We need much more attention focused on evaluating chartering as a policy. Knowing how well charter school students on average are performing does not answer the most important questions policymakers have about where to go with their charter policies.

4. Charter schooling represents an experiment worth continuing – and refining to improve quality further over time.