Data from the 2019 National Assessment of Educational Progress indicates that only one-third of fourth and eighth grade students are able to read proficiently on grade level. Despite a well-established research base indicating that all students benefit from explicit, systematic code-based instruction, many teachers lack the knowledge about the English language necessary to implement these structured literacy methods in the classroom. Professional literacy organizations such as the International Dyslexia Association (IDA) have developed knowledge and practice standards to guide evidence-based teacher training in code base methods, however, research that examines whether professional development programs that follow codified teacher preparation standards increase teacher knowledge in reading content is limited. The purpose of this quasi-experimental, one group, pretest-posttest study was to examine the impact of one online, IDA accredited professional development program on teacher knowledge of English language structures. The program could be completed in varying time frames and offered the opportunity for participation in virtual communities of practice. Composite pretest and posttest Reading Assessment Survey (RAS) scores from 61 teachers were compared to determine if teacher knowledge increased significantly following participation in one online, IDA accredited professional development program. Analyses were also conducted to determine if there were significant differences in RAS gain scores depending on rate of program completion, and whether there was a significant relationship between frequency of participation in the virtual community of practice and RAS gain scores. Results indicated that RAS composite posttest scores were significantly higher than RAS composite pretest scores. There was not a significant difference in RAS gain scores depending on rate of program completion, and there was not a significant relationship between frequency of participation in the virtual community of practice and RAS gain scores. These results indicated that the online, IDA accredited program in structured literacy was effective in increasing teachers' knowledge of the constructs needed for structured literacy instruction, and represents a high-quality PD opportunity for teachers of reading. [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.]