I recently completed a distance supervision contract for a BCBA candidate. As part of her training, she completed a self-rating scale on the BACB 4th edition task list as a pre-supervisory period and post-supervisory period test. 
This is one way I try to make supervision as data-based as all other behavior analytic services I offer! Here are her awesome results!

These graphs served as positive reinforcement for both the supervisor and supervisee to keep up the good work! I know she is going to do great things as a BCBA in the not so distant future!

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She went from mastering knowledge of only 76% of all BCAB 4th edition task list skills to almost a perfect score after supervision!

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This shows the data broken down into the component sections of the BACB task list. Some areas made huge improvements!

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The foundational knowledge section was definitely the most difficult for the supervisee. But after working hard, studying, practicing, and engaging with behavior analysis literature, she is ready to face the BCBA exam this fall!