Special Education teachers serve students who are struggling in mathematics and continue to fall further behind each year. Educators are faced with the challenge of selecting the most effective program for assessing and teaching mathematics that will promote mathematics achievement for students who are served in resource settings. The KeyMath-3 Essential Resources (KeyMath-3 ER) is a mathematics program aligned with National Council of Teachers of Mathematics standards, which incorporates research-based practices for teaching mathematics to students with disabilities. This study utilized the KeyMath-3 ER program as an intervention with five second-grade students with various disabilities receiving their mathematics instruction in a resource setting. The results demonstrated the potential usefulness of KeyMath-3 ER as an effective program for students in a resource setting. The one outlier was a student with autism who did not show significant progress demonstrating a need for further research to assess the effectiveness of using this program with like students.