When I first scanned the report it sounded reasonable, then I noticed something odd... the main point in the conclusion which indicated the prep schools had similar graduation rates to direct admits referenced different time periods than the supporting tables that showed demographic representation.
Does not pass the sniff test... there may be reasons to use different time periods but they need to note why. Especially since the metrics they are referring to were available in all the data sets.
So this comes across to me like someone cherry picked the data, and would not pass a college prof sniff test, much less the hard nosed types I deal with daily.
So then I look for the author... there is none. It's an "issue" paper by the diversity office, which (surprise) indicates the prep schools are doing a great job supporting diversity requirements.
Which they may be, I don't have an axe to grind there. But this paper sure does not prove it, it's just sloppy analysis.