Evolution is a central principle of biology. However, key aspects of evolution can be very difficult to model in a classroom setting. Two such key principles are (1) how the accumulation of small, relatively minor modifications can lead to the diversity of life over extended periods of time; and (2) how closely related genomes between different organisms can yield such dramatic differences in patterning and phenotype. The second aspect is explained largely by evolutionary developmental biology (“evo-devo”), whereby tiny modifications in when, where, and how much the same genes are used during development can lead to dramatic differences in the adult. Developmental construction, using similar building tools, can lead to the formation of a large variety of forms. Here, I describe fun, inexpensive, and simple methods using drawings and Legos by which students can actively generate understanding of descent by modification and evo-devo. Specifically, students learn how the same genes, used in different ways, can lead to “endless forms most beautiful” as originally phrased by Darwin himself. With the accompanying guided discussion, these activities also illustrate other key principles of evo-devo such as combinatorial and modular enhancers, Von Baer's principles, and genetic and morphological homology.