This document proposes a "learning-based evaluation" method for assessing visual analytics systems. The goal is to directly measure how much knowledge users gain from interacting with a system. It involves giving users a new but related task after use and testing their proficiency. This allows evaluating if the system helped users learn about the interface, data or problem domain. The document outlines applying this to the VAST Challenge and integrating it with other evaluation methods. It argues this approach matches what clients like agencies need to see to adopt systems.