This study invited small groups to make several arguments by analogy about simple machines. Groups were first provided training on analogical (structure) mapping and were then invited to use analogical mapping as a scaffold to make arguments. In making these arguments, groups were asked to consider three simple machines: two machines that they had built, used, and made measurements with and one that they had not yet studied. Finally, groups were to produce an argument in favor of the machine that worked most like another machine. Seven of these approximately 50-minute analogical-mapping-based comparison activities were given to 55 preservice elementary teachers working in 15 small groups over 7 weeks. When used as a scaffold for argumentation in small groups, these activities were found to generate a need for discernment, which allowed for simple machines and their parts to be understood in and connected to the context.