Stromatolites are the rocklike structures produced by "microbial mats"--communities of microorganisms only a few millimeters thick--as they trap, bind, or precipitate minerals. This article provides activities and assessment ideas to help teachers incorporate stromatolites in their classrooms. It relates the study of stromatolites to the three dimensions of "A Framework for K-12 Science Education" (NRC 2012). The article invites science teachers to use stromatolites in the classroom for all three dimensions of the new "Framework" and to address some of the big ideas of earth science.