The purpose of the study was to investigate the effectiveness of teaching a three-step cognitive strategy (TIP) using the schema broadening procedures on functional mathematical problem solving skills of young adults with intellectual disability (ID). We randomly assigned 14 learners with ID to the control and experimental group before the intervention. An instructor delivered a series of 12 lessons to students in the experimental group following the procedures developed by the researchers. After the intervention, students in the experimental group outperformed the control group with regard to their ability to (a) use the strategy to calculate tip and bill amounts and (b) transfer the use of the strategy to solve novel problems in the same schema. In addition, five students in the experimental group successfully generalized the use of the TIP strategy in a real-life situation one week after the intervention.