Natural selection is a widely misunderstood yet critical element to understanding evolution, a concept already fraught with controversy and challenges to its instruction. This necessitates creative methods to improve student learning in this area. A constructivist mini-unit incorporating simulation-based games involving a population of imaginary creatures called Chukwins was created to maximize student learning and motivation. It was tested in one elementary and three junior high classrooms in different locations. Changes in understanding were assessed before and after treatment. Surveys and interviews provided additional evidence on students' attitudes toward the mini-unit and its impact on their learning and engagement. Students made statistically significant improvements on assessments regarding natural selection, reducing their number of misconceptions and slightly improving their ability to apply it. Retention scores indicate that the changes are long-lasting.