Evolution is a central, unifying theory for all of life science, yet the subject is poorly represented in most secondaryschool biology courses, especially in the United States. One challenge to learning evolution is that it is taught as a conceptual, retrospective subject with few tangible outcomes for students. These typical passive learning strategies lead to student disengagement with the material and misunderstanding of evolutionary concepts. To promote greater investment and comprehension, we developed EvolvingSTEM, an inquiry-based laboratory curriculum that demonstrates concepts of natural selection, heredity, and ecological diversity through experimental evolution of a benign bacterium. Students transfer populations of Pseudomonas fluorescens growing on plastic beads, which selects for biofilm formation and mutants with new, conspicuous phenotypes. We introduced our curriculum to four introductory high school biology classes alongside their standard curriculum materials and found that students who learned evolution through EvolvingSTEM scored significantly better on a common assessment targeted to Next Generation Science Standards than students taught only the standard curriculum. This latter group subsequently achieved similar scores once they too completed our curriculum. Our work demonstrates that inquiry-based, handson experiences with evolving bacterial populations can greatly enhance student learning of evolutionary concepts.

19 20 Evolution is a central, unifying theory for all of life science, yet the subject is 21 poorly represented in most secondary-school biology courses, especially in the United 22States. One challenge to learning evolution is that it is taught as a conceptual, 23 retrospective subject with few tangible outcomes for students. These typical passive 24 learning strategies lead to student disengagement with the material and 25 misunderstanding of evolutionary concepts. To promote greater investment and 26 comprehension, we developed EvolvingSTEM, an inquiry-based laboratory curriculum 27 that demonstrates concepts of natural selection, heredity, and ecological diversity 28 through experimental evolution of a benign bacterium. Students transfer populations of 29Pseudomonas fluorescens growing on plastic beads, which selects for biofilm formation 30 and mutants with new, conspicuous phenotypes. We introduced our curriculum to four 31 introductory high school biology classes alongside their standard curriculum materials 32 and found that students who learned evolution through EvolvingSTEM scored 33 significantly better on a common assessment targeted to Next Generation Science 34Standards than students taught only the standard curriculum. This latter group 35 subsequently achieved similar scores once they too completed our curriculum. Our work 36 demonstrates that inquiry-based, hands-on experiences with evolving bacterial 37 populations can greatly enhance student learning of evolutionary concepts. 38