Homework's fun! Well... it is when you do a watercolour page of eyes.
Actually, in my experience, it's not just the eyes that are so important in portrait painting, it's the mouth. The eyes are round and colourful, so they's interesting and fun to paint. But the mouth... one extra bit of line or colour can change the whole expression of the face. The mouth is tricky. So subtle. I don't think I should shy away from doing a page of mouths next. ; )