Why boarding schools produce bad leaders

While it doesn't address the proof you mentioned, the author writes this paragraph concerning studies which could be clues and/or are interesting studies on their own for education in general:

"Recent evidence from neuroscience experts shows what a poor training for leaderships this actually is. In short, you cannot make good decisions without emotional information (Professor Antonio Damasio); nor grow a flexible brain without good attachments (Dr Sue Gerhardt); nor interpret facial signals if your heart has had to close down (Professor Stephen Porges); nor see the big picture if your brain has been fed on a strict diet of rationality (Dr Iain McGilchrist)."