Not an insider at HP, but assume the money will come from being handed the keys to the feeder program for Highland Park. In Texas, Highland Park high school is broadly referred to as the nicest private school in the state - except it is public.
It is the single high school for 2 of the 3 most expensive neighborhoods in Dallas. Significant number of families with 10,000 sf houses on 5-10 acres five minutes from downtown Dallas. Lots of dough to throw at club and rec league that creates an awesome funnel of talent for HP high school. Of course they lose some of those kids to Dallas Jesuit, St. Marks and Episcopal School of Dallas, but they keep plenty.