I don't think that DA is trying to set a higher bar (i.e. higher than 99.9%). I think that they're probably trying to focus on slightly older kids, perhaps for social and emotional reasons, perhaps because of the issues with study skills and managing workloads. Perhaps because it will make for a more cohesive group if they have less of a spread in age.
At any rate, it seems to me that what they are looking for are kids who are working at a high school level, and probably at (or close to) middle school age. I'm not sure if their information still refers to kids working at a middle school level, but any kid who gets those scores on the Explore is working above a middle school level, at least in terms of content.
