I have given this assignment as homework and in class.  I find that doing intensity with adding white and adding white really helps students learn how to mix.  It is best done in class with novice students, but can be good reinforcement and further practice for intermediate students to do for homework to develop mixing skills.  I inherited this assignment from Jo Zider who was always very good at teaching students technique.  Here you can see the same exercise performed in dry media (oil pastel) above and acrylic (wet media) below.