Hmm... To me, a master of rationality might seem to be able to debate fairly well with other heads of powerful schools, such as philosophy and physics. I myself can pose some interesting questions to physics knowledgeable people, and refute offhand philosophical stupidity in a stride.

To test students for rationality I guess is easier to test for debiasing, by making classical bias experiments?

I need to mull this over with my fellow Bayesian conspirators.