Are you talking about the US? The statistic suggests that you're talking about somewhere specific. I'll assume the US.
You have several claims that are not obviously related. That's not to say that I disagree with any of them, though I probably would disagree with the implicit claims that relate them, if I had to guess what they were. One red flag is the conflation of public and private schools, which have different goals and methods. The 6 year graduation rate is really about public schools, right? But then you invoke selective schools in the last paragraph.
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