"intrinsically unschoolable" might be going to far, but I think it's generally agreed upon that children in poorly performing school districts are (on average)

"intrinsically unschoolable" might be going to far, but I think it's generally agreed upon that children in poorly performing school districts are (on average) more difficult to teach. It's also generally agreed upon that students have an impact on their peers. This is the whole rationalization for better integrated schools in the first place. We can certainly debate how many (as a % or raw number) challenging students a "good school" can import before overall quality begins to degrade. But I don't think that it's especially controversial to say that degradation will happen at some point.