The purpose of this study was to explore secondary mathematics teachers' perceptions of detracking including benefits, challenges, and needed support as well as their individual and collective efficacy beliefs for teaching in a detracked class. Shifting to heterogeneous and inclusive secondary mathematics classes is a significant shift from past practice, and thus, teachers' beliefs about their individual efficacy for such a change can impact the success of detracking reform. By understanding the areas of strength and areas for growth through the lens of individual and collective teaching efficacy, leaders can better understand the professional learning and support needed to sustain detracking reform. A convergent, mixed-methods design was used to analyze quantitative data from Likert-type scale items measuring individual and collective efficacy and items measuring perceptions of stakeholder support of detracking as well as qualitative data from open-response survey items and individual interviews. Participants identified more challenges of detracking than benefits. Furthermore, benefits were described idealistically and with hope for the future, while challenges were described in more detail and as intensification of already existing challenges. Participants showed understanding of the purpose of detracking but were not in agreement that this particular reform was the right way to achieve that purpose. When reflecting on their confidence and competence for teaching in a heterogeneous mathematics class at the high school level, participants had the highest perceived efficacy for individual efficacy for instruction. Teachers expressed low confidence that stakeholders would support detracking reform. For personal support to implement detracking, teachers requested both professional learning and structural changes that they felt would give them the opportunity to better serve a diverse group of learners in their classroom. Three major themes emerged from the data around the intersection of content knowledge and pedagogical skill, student motivation for learning, and stakeholder support for detracking. The significance of these themes contributes to the existing literature on detracking and suggest the following: 1. Successful differentiation practices in a detracked mathematics class may require structural changes to secondary mathematics. 2. The practice of labeling students may contribute to a fixed mindset incongruent with the goals of detracking reform. 3. Detracking at the secondary level is uniquely challenging when students have spent the majority of their elementary and middle school education in tracked settings. Based on these implications, recommendations for key stakeholders and future research are provided. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]