In my Biology curriculum, natural selection and evolution are heavily stressed. To help students understand these concepts, I use the HHMI BioInteractive on the Making of the Fittest. The lesson plan on Rock Pocket Mice is very good. My 9th grade Biology students enjoy learning about these furry little mice and how a change in the environment has changed their allele frequency over time. There’s a pre-test as well as a post-test to gauge student’s understanding.