It is good to know that Google is having courses about AdSense. Check out Google online course title Optimizing AdSense. The course consists of 17 video lessons with each about 2 to 4 minutes long. There are also some activities and assignments available for practice. Be sure to register and take the course if you are interested.
Although the course is design for beginners who are just starting to use Google AdSense, it is still a good revision and practice for those who are still looking for ways to improve their Google AdSense earning. There is also a forum section which participants can ask questions. I suppose a lot of AdSense publishers will be aiming for this section as they can ask question specifically which related to their blog or website. Participants who successfully complete the pre and post assessments will receive certificate of completion. Although it is not a certification, you can still show off by posting it on your blog or website.
P/S: Back in those days, I still remember we need to pay for information about how to maximize Google AdSense earning. Now this information is free.