Jakob Nielsen wrote in his newsletter about field testing:

I got a nice bag from Briggs & Riley for my upcoming trip to Europe. An enclosed brochure says that ‘If your luggage is ever damaged (even if it was caused by the airlines) we’ll fix it, free of charge. By examining every damaged piece, we see how to continuously improve and refine our bags.’ Studying why things go wrong is one of the best ways of making things go better in the future.

He went on to give an e-commerce example:

For example, an e-commerce site should research why customers return purchases. Often, you’ll discover that your product pages are at fault, for making users order the wrong stuff. Fixing the website will not only reduce costly returns processing, it will also increase your conversion rate, because most users won’t buy if they’re uncertain of what they will get.

Doesn’t what applies to abandoned shopping carts, returned purchases, and damaged luggage apply equally to online courses? If you lose students, they are gone. No feedback. No end-of-class evaluation. Yet their feedback might be the most helpful in knowing how to improve a course.
If your students struggle, then what can you do differently in the design, presentation of material, assignments, etc. to better support their education? Field testing and continuous improvement are far too often not included in schedules. Jakob’s story shows a very different attitude, one that we might all benefit from adopting.