In learning science, most measures of outcomes eventually seem to boil down to that. You've got a few other ideas, like measuring the degree someone is participating in a community of practice for example, but most of the time you have to look at a change in performance, artifacts produced, or attitudes (as evidence by communication in certain settings, which almost resembles response to stimulus). If none of things things occur, it's controversial to say if learning has occurred.

I say controversial, you do have the contructivist approaches, where a learner basically is expected to build up their own network of meanings and associations in the new field. Constructivism without any behaviorist element tends to be less measurable, which is part of the reason it is controversial. This also takes a lot of time and resources as a teaching method. (And I might point out, the goal for the end result is still expert performance, and I am not sure it is not just reaching around the back of your head to touch the nose of behavioral changes after all).