The charter school has 75 kindergarteners every hear, but every grade after that has one-third of that number. It would seem they are culling the heard to the best prospects.
...
The article addresses that with what I think is a reasonable explanation.
“Parents select the program. It is not based on performance,” Principal Alexandra Prieta said. “They do this in kindergarten or first grade — before students are in the state testing system.”
But not isn't a very satisfying explanation. Why would any parent take their kid out of such a top-performing program at the end of K? I just can't see a 2/3 of parents choosing another school.