This study assessed the effectiveness of modified schema-based instruction (MSBI) in teaching students with autism spectrum disorder (ASD) how to solve additive compare word problems. The study was conducted in Spain, and it involved three students with ASD who were 6, 7, and 9 years of age. A single-case, multiple-baseline across-students design was followed. Results indicated a functional relation between MSBI and improved performance in solving additive compare problems of type difference amount unknown and compare amount unknown, maintained for 4 to 6 weeks post-intervention. Additionally, two students successfully applied their skills to reference-amount-unknown compare problems, demonstrating successful generalization. However, their generalization to problems involving two operations was somewhat limited by difficulties with one of the operations. Social validity data collected from the students' families and teachers indicated that both groups had positive views on the use of the MSBI for mathematical word problem-solving skills.