Researchers and educators are calling for increased use of technology and attention to function concepts in school mathematics. Students often have considerable difficulty gleaning pointwise and global information from Cartesian (R squared) representations of functions, whether they are hand- or machine-produced. Described here is an interactive computer-based learning environment (the Function Explorer) which provides dynamic, linked representations of functions. Representations using tables, parallel number lines, and perpendicular number lines dynamically display ordered pairs of the function. A randomized comparative experiment is described which was performed to test the effectiveness of the number line representations for enhancing student understanding of basic function concepts. Contains 13 references. (Author/MKR)