To test this, you could track down state dept. or Army records and then compare lead levels in country A (where the brats were posted) with later school results. It's a good group to study because they're randomly assigned to posts or bases and come from same s-e background.
Also, this DoD school idea could be combined with my localized-lead-pollution idea. When many military bases were shut down after victory in the Cold War, huge amounts of money were spent studying how badly contaminated each base's soil was with toxins, such as lead. Some of these bases up for closure were in desirable real estate markets, and a big question was how much it would cost to clean up all the scary chemicals the military emitted over the years before people would buy condos there.