The purpose of this study was to investigate the effect of the Concrete Image Spatial Concepts (CISC) instructional strategy on the spatial ability of junior high students. The sample consisted of 125 junior high eighth-grade students in the Taipei area. The participants were assigned to three groups. The experimental group received a 3-week CISC treatment, whereas the two control groups received a 3-week non-CISC teaching. The Spatial Ability Test was used in the pre- and post-test. The results showed significant difference in spatial ability among the three groups, and the spatial ability of the experiment group was better than the control groups. But no significant difference was found among the low, medium and high achievement students in the experimental group. From the qualitative data collected in field observations, it was observed that CISC not only elevated the learners’ operational abilities with mental images but also catalyzed the interactions between 2D/3D representations. It appears that CISC strategy is functional in lowering students’ cognitive load and the complexity of abstract concepts. CISC has also demonstrated its effectiveness in elevating students’ spatial ability through ease in mental image construction.