If you arrived at the class with a novel-in-progress for which you have already done a significant amount of writing, you may wonder how to approach assignments. Here is my advice:
If the assignment covers something you've already written, I recommend reading the lesson and then going back to the scene or chapter, rereading it, and seeing if there's anything you feel compelled to add or subtract. You can use the assignment as a prompt to revise and expand existing scenes.
I tend to revise as I go. This means that, by the end of a draft, some scenes will be more polished than others. That may slow the draft down a bit, but it makes revision easier. If you like the revise-as-you-go approach, take the assignments as an opportunity to fine-tune and polish your work, adding texture and thematic elements, streamlining sentences, fleshing out characters and settings.
If, on the other hand, you feel comfortable with the scene/chapter as it is and don't want to revise it yet, use your writing time that week to work through your Scene List. You'll find a lecture on the Scene List, but here's how it works in a nutshell:
When I get about 50-75 pages into a novel and I've begun to better understand where it's going, I create a running scene list. This is just an informal list of 10 or so scenes that I believe the novel needs, arranged approximately in the order in which they will appear. The list can be as skeletal or as expansive as you want. Mine tend to be quite abbreviated. For example:
Then, on days when I sit down without a clear idea of what to do or without feeling a specific direction tugging at me, I go to my scene list and tackle one of those.
Another thing you can do is write a list of questions you have for yourself--things you don't know or haven't yet revealed about the character, things you are still working out about your theme or your protagonist's background or your setting--anything, really. Then, during your writing time, if you get an assignment you've already completed, you can write a passage that answers one of these questions.
As for word count, any scene or chapter that you have seriously revised during the week can go toward your word count for that week.