Research Findings: Evolution by natural selection is often relegated to the high school curriculum on the assumption that younger students cannot grasp its complexity. We sought to test that assumption by teaching children ages 4-12 (n = 96) a selection-based explanation for biological adaptation and comparing their success to that of adults (n = 30). Participants provided explanations before and after a 10-min, analogy-based tutorial illustrating the principles of variation, differential survival, differential reproduction, inheritance, and population change. Although younger children (ages 4-6) showed minimal evidence of learning these principles, older children (ages 7-12) showed robust evidence of doing so, learning them at rates equivalent to adults. Participants of all ages, however, provided nonevolutionary explanations for biological adaptations (i.e., explanations referencing need, growth, and creation) nearly as often at posttest as they did at pretest. Practice or Policy: These results suggest that older elementary school-age children can be taught evolutionary concepts but that learning such concepts does not lead to the automatic replacement of nonevolutionary views of biological adaptation, which must be addressed separately.