It's not just selection bias, though. Charters, having distinctive education styles, will be more appropriate for some students and less appropriate for others.

It's not just selection bias, though. Charters, having distinctive education styles, will be more appropriate for some students and less appropriate for others. The other layer of "selection bias", then, is that parents/children will be more inclined to charters that seem more suitable for their own needs. For example, in MN, we have a number of Somali-language bilingual charters for our massive Somali immigrant population. Fantastic option for Somali immigrant kids. Not so fantastic for other kids. That's not just selection bias on parental involvement, that's appropriate environment for the kids' needs.