Are you sure the 1 problematic battery is in good shape? If the bottom of the batter is bulging even a little, and you are able to properly snap it into place, its balance could be off enough to cause the yaw.
I agree with the concept of introducing them to the TRUST cert through FAA DRONE ZONE so they can read the basics, ask you some questions if necessary ,and take the TRUST test.....then continue with some questions from you students and answers...
I conduct workshops like this, frequently to middle and high school students but also to adults.
I take the opportunity to do the TRUST certification as a group so everyone is a certified recreational pilot. Going through the test together gives...