That's a tough question to answer because "charter school" doesn't have a very specific definition. It's just a publicly-funded school whose charter opts it out

That's a tough question to answer because "charter school" doesn't have a very specific definition. It's just a publicly-funded school whose charter opts it out of some number of the regulations that apply to typical public schools in the same jurisdictions. In some states/districts, they're basically public schools that have an external partner. I taught at such a school in Baltimore. In other places, they're more or less completely independent of the district that funds them. Anywhere on that spectrum, you can cherry-pick successes and disasters. But certainly, they have introduced a great deal more complexity and ambiguity in the discourse of education. Much of the negativity towards charters comes from a skepticism that is difficult to fully inform. So people are forced to take the shortcut of deciding whether they are for or against "charter schools", broadly speaking. Fact is, not everyone has time to become an expert, in order to hold more nuanced opinions. I prefer to frame the debate around the "school choice" movement, which is broader idea that districts should work more like marketplaces or laboratories for education. I'm very skeptical. For one thing, the "choice" that results isn't free and isn't equally distributed. For another, it tends to centralize the blame for poor outcomes on poor performers in the district, rather than systemic issues. Yet, most of the poor performers are the very schools that have the highest risk students, because these are the same students unlikely to have the agency and social capital to effectively exercise their choice.