This handout is really helpful when teaching students how to see commonalities among characters. I give them a bunch of characters (see my Flash Cards category for some ready-to-go sets), and ask them to put them into groups based on either radicals or sound. For example, students might group 吗，呢，and 可 based on the mouth radical, or 吗，妈， and 麻 based on the pronunciation "ma." This activity can be used any time, in a number of situations. It's great for early finishers, too!