The above post was with somewhat old data; I downloaded the relevant database from california, and using the most recent numbers (2014) updated things[1]. There are fewer schools because I originally included schools that were not geographically based, as we are talking about geographic segregation. The blue dots correspond to % hispanic students, the pink is % qualifying for free/reduced school lunch, and yellow is % English learners. The Y axis is state standardized test scores.

There are now not any schools with less than 20% hispanic student populations (there is still a charter school with under 20% hispanic, but it was excluded per above), but there is a huge hole between 45% and 75% hispanic, and 6 out of 10 are 80% or more hispanic. If children were assigned randomly to these schools, one would expect a normal distribution around the population mean.

And to clarify, all of these schools are within a single school district and pull from the same funding source.

1: http://imgur.com/a/8iLt9