The paper describes the rationale and 10-day implementation in a 5th-grade classroom (n=19) of an experimental ratio-and-proportion instructional design. In this constructivist-phenomenological design, coming from our theoretical perspective, design research, and domain analysis, students: (1) link "real-world" and "mathematical" objects reciprocally through classroom enactment of word-problem situations vis-a-vis guided reading/writing of spatial-numeric inscriptions; (2) interpret and invent rate, ratio, and proportion texts as patterned cells in and from the multiplication table; (3) revisit and consolidate addition and multiplication as conceptual domain foundations. Students of diverse ethnicity, SES, and mathematical competence engaged successfully in discussing and solving complex problems, outperforming older students on comparison items. (Contains 1 figure and 1 table.) [For complete proceedings, see ED500859.]