All teachers should have learned early in their career that periodic assessment is a good thing. Before you teach children multiplication, you give them a ten-minute test on addition. If they haven't mastered multiplication, there is no point in plowing ahead.
The same thing is true when teaching judo. For many years, I had a problem with teaching beginning students to do forward throws, especially very young kids. One day, I had them do these simple agility ladder drills (I was at a more affluent club then where we could actually afford stuff) and I realized that the kids had trouble with the basic movement of just twisting your body around in the air.
So, in every class now, from time to time I do some drills like this. Again, we do it in a relay race format, to make sure the students are putting out an effort, plus races like this are a good way to instill a competitive spirit without anyone getting hurt.
Since we have no agility ladders, I just put belts on the mat and the students are to go as fast as they can down the line pivoting and then back again.
Here is a few seconds in a clip to show you how it looks.