This time I took a picture of this simple still life to make it easier. Also this way everybody have the same "view" of the subject. We have poor possibilities to do big or nice still life installations in the space we meet to work. So I find this solution quite good for now.
Personally I prefer to work from life though as I don't get the same emotions when I work for photos. In my opinion emotions are what painting is about, so we should search for those every time we settle down work even when we only have a photograph in hand.
In this assignment they are supposed to paint only in values. And do this by mixing the three complementary colors (taking dark "primary" colors; to obtain real darks).
Several attempts of the same exercise on different papers is good to do, or start over if you are not happy with the result, and of course try to do better what didn't work.
Each paper might give a different reactions and result and you can also feel more comfortable with a particular paper compared to some others.
Mix enough paint and pay attention to the exact color you get by observing it's temperature and hue, before painting, or you might get a painting in too many different kinds of colored blacks and grays.
The task is to stick to one color, and that's also the difficulty when searching for the same hue.
Don't give up with patience and practice you'll get it.