The purpose of this study was to examine the relative effectiveness of two different learning modes; namely, a computer animation self-directed learning approach and a paper version of the self-directed learning approach, to 5th-graders' number sense development. Two 5th-grade classes, 30 students each, were selected from a public elementary school in southern Taiwan and randomly assigned to the computer animation experimental group [CAEG] and the paper-version group [PAG]. The major finding indicated that students in the CAEG group had better performance on number sense and showed more frequent uses of number sense than students in the PAG group. Implications for the uses of computer animation self-directed learning activities are discussed.