In species that reproduce sexually, an individual's fitness depends on its ability to secure a mate (or mates). Although both males and females are selected to maximize their reproductive output, the mating strategies of the two sexes can differ dramatically. We present a classroom simulation that allows undergraduates to actively experience how differences in parental investment lead to differences in reproductive behavior. Students will understand why males generally compete for mates whereas females generally choose among mates. The activity provides a foundation for exploring advanced topics in animal behavior, or it can be adapted for introductory biology courses.