They cherry pick the better students so they can put out propaganda that charter schools produce better results. In fact, there isn't a single case I have seen where, when normalizing for demographics and revenue per student, a for-profit charter has produced better results.
In my state, they are able to play a game where they keep the students enrolled until Oct 1. Then the students that aren't scoring well enough, are behavior problems, or otherwise don't help feed the propaganda machine are "counseled out" to the public district. But the charter still gets FULL PAYMENT for that student as if he attended the full school year and the public district doesn't get a dime, yet is compelled to accept all the counseled-out students.
Every year they open another charter or two or 10, all playing this same bullshit game. That leaves the public district with about 2/3 the funding per student that the charters receive. So parents become dissatisfied and get in line for the next batch of charters.
That means that the public district has excess capacity. They can't have teachers with classes of 12 students and Principals with 15 teachers, so they have to consolidate. But the district is just as large as it ever was, so they have to spend about the same money on buses, gas and drivers even when the student population is dropping.
And then they have to lease those empty buildings for $1 per year to any charter that raises its hand, but the public district still has to pay millions of dollars every year for the upkeep on those charter buildings and they don't get a penny for it (well OK, they get 100 pennies per building, but nothing else.)
Talk about a rigged system, these goddamned Republicans (with loads of help from Democrats) have this system rigged from every angle.
On top of that, our previous State Superintendent (R) got caught rigging the test scores for many of the charter schools that were failing despite the huge resource advantages they had over the public districts. Fortunately that ahole got upended by a grass roots campaign that shocked the system by electing the only Democrat in statewide office here. That cheating Superintendent moved to Florida where he now works for one of those for-profit charter corporations. You can never kill the cockroaches. They just find new places to hide.