If you have been using Khan Academy in your classroom both before and after the change, would you be willing to post your feedback in the post I made to accumulate teacher feedback on Khan Academy Reimagined?

(I'm just another user, and I don't know if KA will use the feedback, but I think it's worth trying.)

I can understand why this would be frustrating, especially after using Khan Academy successfully in your classroom for so many years. If mastery challenges were an important part of your 3-step approach, removing them would definitely disrupt the way you structured practice and review. I hope Khan Academy takes feedback from experienced teachers like you seriously and considers bringing back the functionality in some form.

If KA cared what classroom teachers thought, they would have had some classroom teachers test KA Reimagined before forcing it on everyone, but there's no indication they did that.