Number comparison is a fundamental skill required for academic and functional mathematics (e.g., time, money, purchasing) for students with disabilities. The most commonly used method to teach number comparison is number lines. Although historically paper number lines are used, app-based number lines may offer greater flexibility. This study compared using paper-based and app-based number lines to teach number comparison skills to students with intellectual disability using a single-subject alternating treatments design. Three secondary students with intellectual disability participated in a classroom setting during baseline and intervention phases and a simulated grocery store setting during generalization phases. Both the adapted paper-based and app-based number lines were effective for students with intellectual disability. However, the app-based number line was slightly more effective in terms of accuracy and completion time during number comparison and price comparison tasks.