Investigated the development among fourth-graders of two-dimensional space concepts within a mathematics unit on grids, coordinates, and rectangles. Found that students' knowledge of grid and coordinate systems related to levels of competence in number sense, spatial-geometric relationships, and the ability to discriminate and integrate the two numbers constituting a coordinate pair and two axes constituting a coordinate plane. Significant learning aids included computer representations and teacher and computer scaffolding. (Author/KB)