The purpose of this study was to investigate elementary children’s conceptions that might
serve as foundations for integer reasoning. Working from an abstract algebraic perspective
and using an opposite-magnitudes context that is relevant to children, we analyzed the
reasoning of 33 children in grades K-5. We focus our report on three prominent ways of
reasoning. We do this by describing and analyzing the responses of three particular children
(in Grades 1, 3, and 5) who exemplify these ways of reasoning. We view each of the three
ways of reasoning as rich and interesting, and we see relationships of each to formal integer
reasoning. At the same time, we view these ways of reasoning in terms of increasing levels
of sophistication, potentially belonging to a single learning trajectory. Thus, we see the
roots of more sophisticated integer reasoning in children’s early intuitions about opposite
magnitudes.