Even with basic material, you can offer a wide variety of different drills and exercises. Mix it up and people won't get bored.
Let's say, to give a very simplified example, your white belt curriculum is one form, roundhouse kick, straight punch and knee strike. Everybody in the class has already learned basically how to do those 3 striking techniques, but needs more practice. You have 12 people in the class and 3 punching bags. Here's a sample class.
First, of course, warm up, stretch, do your form.
Next, you have everyone get with a punching bag, and everybody takes turns doing 25 roundhouse kicks, 2x each. Then 25 punches, 2x. Next, they do a combination of roundhouse kick and straight punch 5 times on each side. Then repeat that with roundhouse-knee strike and punch-knee strike. Then you put 30 seconds on the clock and have everybody just strike continuously, mixing up the techniques, 2x.
Next, everybody gets with a partner and grabs a shield-style pad (you might need to have 2 pairs switch off using one pad depending on how much room/pads you have). One partner holds and the other partner does roundhouse kicks down the room. Then switch holders and go back the other way. Do the same thing with punches and knee strikes. Then have them do the same thing with a mix of those techniques.
That class will not be boring.