Recent studies have analyzed the cognitive demands of solving problems in genetics, focusing primarily on the Piagetian schemas of combinations, proportions, and probability. Based on data from these primarily correlational studies, some authors have argued for the elimination of classical genetics from the high school curriculum. The critical review of the literature presented in this article reaffirms that formal-operational thought is conducive to successful genetics problem solving. The weight of the evidence to date, however, does not support the position that formal operational thought is strictly required for solving typical genetics problems. Arguments are therefore presented in support of the inclusion of genetics and genetics problem solving in high school biology. Implications of this analysis for the selection of appropriate content, problems, and instructional techniques for genetics instruction for nonformal students are presented.