From The Death and Life of the Great American School System, by Diane Ravitch:
Our schools cannot improve if charter schools siphon away the most motivated students and their families in the poorest communities from the regular public schools.
FedUpMom again: One of the claims of the charter school movement was that charter schools would improve the public schools, through the magic of competition. This was always a ridiculous idea. You could throw me into a race with Michael Phelps, but would I suddenly become an Olympic-quality swimmer? Of course not.
What the charter schools can provide is an escape hatch from the crummy public schools. People with enough money have always had an escape hatch, namely private schools. Those with less money can escape to Catholic schools (which Diane Ravitch seems to like), or, with a great deal of luck, a good charter school.
If this means that the public schools lose some of their best students, too bad. It is their own fault if the best families in their district are desperate to keep their kids out of public school.