In reviewing the six articles within this "Instructional Science" special issue, we are reminded of Schoenfeld's ("Educ Res" 45(2):105-111, 2016) review of American Educational Research Association president-authored papers for the centennial celebration of AERA. There, he succinctly unveiled the content focus of AERA research in the first half of the twentieth century: "there is content to be mastered; it is the schools' job to help students master it" (p. 106). Yet, like Schoenfeld says, "A century later, we hear the echoes of this functionality in the calls for '21st-century skills,'" (p. 106), and the "skills" of the twentieth and twenty-first century would hardly know each other. Twentieth century skills, as represented in the accounts from past AERA presidents, were product-oriented, like accurate copying and precise handwriting. Twenty-first century skills are focused on creativity, ingenuity, critical thinking, and the like. In our primary research space, mathematics education, problem solving, sense making, and conceptual understanding dominates in the twenty-first century, whereas procedures dominated teaching and learning mathematics in the twentieth century.