It is true that learning can happen from change in performance. When a student is learning, they are expanding their mind to accept new ways of doing something, and to be open to new information. When it comes time for application of that new information and the new ways in which they learned to tackle a problem or do a task, they have an opportunity to display those new skills. The performance characteristic that indicates learning is improvement. If a student improves, even slightly, after they are taught something, then it shows that they have learned something.