In the Public Interest has published a new report (pdf) on the impact of charter schools and public school funding in CA:

In a first-of-its-kind analysis, this report reveals that
neighborhood public school students in three California school
districts are bearing the cost of the unchecked expansion of
privately managed charter schools. In 2016-17, charter schools
cost the Oakland Unified School District $57.3 million, the San
Diego Unified School District $65.9 million, and Santa Clara
County’s East Side Union High School District $19.3 million. The
California Charter School Act currently doesn’t allow school
boards to consider how a proposed charter school may impact
a district’s educational programs or fiscal health when weighing
new charter applications. However, when a student leaves a
neighborhood school for a charter school, all the funding for
that student leaves with them, while all the costs do not.