An important yet difficult question to answer is: how do we know if someone has improved?
It might sound like an easy question, but trying to quantify learning is a difficult task – particularly when improvements are small and specific.
In the Motor Control and Learning textbook, Richard Magill described 5 characteristics of learning. These 5 characteristics should guide the measurement of performance and learning.
Can the person perform the skill at a higher level?
Is performance becoming increasingly more consistent?
Is performance more resistant to perturbations, both internal and external? Internal perturbations include stress, such as when performing under pressure. External perturbations include environmental factors, such as the wind or an obstacle.
Is improved performance retained over a longer period of time?
Is performance more adaptable to a variety of contexts? Contexts can vary based on the individual (e.g., emotional state), the task (e.g., speed or distance of movements) or the environment (e.g., weather).
Magill, R. A. (2007). Motor Control and Learning: Concepts and Applications (8th Ed.). New York, NY: The McGraw-Hill Companies.