Venn diagrams can be a great way for students to compare information -- but for high school, they lose some of their value because they don't focus the comparison well enough. This graphic organizer solves that issue. Though designed with high school in mind, it could also work well for middle school students.
How to use it: When having students make a comparison between two things, first have them label the circles with the two topics/subjects they are comparing. Then, have them think of three categories through which to focus their comparison -- or, you might instead pick the categories for them. Students label the first, middle, and bottom sections of their diagram with the categories they'll be looking at, then proceed as their normally would with a Venn diagram (i.e. putting differences and similarities in the appropriate sections within the circles).
For example, if students were using this graphic organizer to draw comparisons and contrasts between the Maya and Inca civilizations, they might have categories for Economy, Government, and Religion. They would label one circle "Maya" and the other "Inca," then label the sections "Economy," "Government," and "Religion." With their organizers now set up, they would then proceed to fill them in with information.
This graphic organizer works very well for students when they are note-taking, brainstorming, or writing comparison essays. I also occasionally use these on tests as an alternative to a short essay question.