This mixed methods study addresses special education teachers' (SETs) knowledge and beliefs about specially designed instruction for reading, individualized education program (IEP) development, and aspects of future professional development opportunities that are supportive on these topics. Special education teachers are the primary authors of the IEP and require ongoing training in best practices for specialized reading instruction and IEP development to ensure compliance and quality of special education services for students with disabilities, but more guidance is needed to determine the type and qualities of supports that SETs need to complete these tasks. Special education teachers (n = 55) from a public school district in Illinois completed an online survey to gather information about their knowledge and beliefs about literacy instruction. They then attended a three-hour, online, professional development workshop on best practices in specialized reading instruction and IEP development. Following the workshop, a subgroup of SETs (n = 7) participated in semi-structured focus group interviews to gain additional insight into SETs knowledge and beliefs. Concurrent mixed methodology was used to guide parallel data collection. Statistical analysis of the quantitative survey data was conducted, and qualitative analysis of the focus group video recording was completed to determine themes. The two data sets were merged and revealed that while SETs feel prepared to implement SDI for reading and develop IEPs, existing gaps in their knowledge base still exist. Different knowledge and beliefs were also noted between SETs in more inclusive settings and those in self-contained settings. Findings concur with existing literature recommending that SETs need more training in specialized reading instruction and related IEP development. Results suggest that PD should be customized, small group instruction including multimodal reference materials or frameworks and multiple opportunities for practice and feedback. These findings also indicate that ongoing coaching is needed to improve and support SETs knowledge and decision-making about SDI for reading and developing IEPs for students with disabilities. [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.]