This study aimed to explore the experiences of special education teachers’ mathematics instruction process and to present suggestions for sustainable special education in mathematics instruction. Seventeen special education teachers were interviewed in this study. Hence, a qualitative research design and content analysis were used. Three dimensions were considered in the interviews, including: teaching mathematics to students with disabilities in terms of teaching methods, manipulatives, and assessments; the mathematics curriculum; and challenges that special education teachers face throughout the process. According to the results, most teachers still use direct or explicit instruction based on the behaviorist approach. All participants stated that they use mathematics manipulatives to help learners perceive mathematical concepts. They also use Individualized Education Programs to assess their students. Participants stated that every disability group and every child need to be considered uniquely since their disabilities and levels vary. Participants also said that they are only able to teach numbers, addition, and some basic geometric shapes due to time insufficiency and crowded classrooms. Almost every participant stated that insufficient time and teacher shortage are the biggest problems of the system. The study has limitations or weaknesses. In this study, since the interviewing method was used, and the findings are the extent of what the participants have indicated, and the statements of the participants are limited to what she/he explained to the researcher. In the study, it is suggested that mathematics teachers and special education teachers should cooperate. In addition, suggestions are made, such as conducting experimental research studies to see the most efficient way to teach mathematics in homogenous groups. Finally, future researchers are advised to focus on the possible consequences of applying constructivist learning theory.