The purpose of this case study was to determine the relative effectiveness of a Combined Activity (using both computer software and hands-on manipulatives that the author produced) in comparison with a traditional mathematics activity (using commercial hands-on manipulatives only) in promoting preschool children’s learning of seriation, logico-classification, counting, and addition. The participants were 37 three to five-year-old preschoolers at two preschools in Florida, U.S.A. The research design was a quasi-experimental (pretest-posttest) control group design, and analysis of covariance (ANCOVA) was used to analyze the data. Results of this study showed that the Combined Activity had a significantly more positive effect on the participants’ understanding of number concepts (F = 6.253, p < 0.05), especially seriation and addition, than did the traditional activities.