If you break this down and draw a section at a time with your students, it seems to improve overall understanding and comprehension. I usually begin with the cross-section of the volcano labeling the "magma", "lava" and "volcano" with only two blank arrows pointing to it and ask the class what must happen for a rock to become an igneous rock - lead them toward the terms "melting and cooling" and write those on the arrows. Then draw the layers of sediment (adding a fossil fish, just to remind the students that most fossils are found in sedimentary rock), labeling the side "layers" and "compacting and cementing" to remind students of the processes involved. Include the two blank arrows pointing to sedimentary rock (one from the igneous rock and one from the area where metamorphic rock will be drawn) and ask the student what must happen before sediments can be deposited into these layers - lead them toward the terms " weathering and erosion" and write those on the arrows. Finally, explain that a cartoon like picture seems to work best for the metamorphic rock to show the processes that are forming the rock. Then draw a rock with flames underneath, labeled "heat" and "magma" and two vise-like pieces crushing the rock with arrows and label "pressure". I always explain that I understand there aren't any flames involved but that the flames help me to remember there is heat involved. Include the blank arrows pointing to the metamorphic rock (one pointing away from igneous and one from sedimentary) and ask the students what processes must happen to form metamorphic rock - lead them toward the terms "extreme heat and pressure" and write those on the arrows. I usually complete this activity by asking the students to write a story or create a comic strip about how a rock can go through all three steps of the rock cycle to assess their mastery.