Crosscut is featuring this story: Charter schools suspending black students at high rates. It's full of accusations and denials.
I'll just add two stories to Charlie's thread that may be of use in this discussion. As the study says, fairly, many charters don't have these issues; it tends to be the "no excuses" charters like KIPP.
From the Edushyster blog: Holding Back to Get Ahead
From Dewey to Delpit: the No-Excuses Charter School Movement