As online training moves beyond schools, corporations and the military, more sectors of the workforce are required to develop professional skills at a distance, without face-to-face interaction with instructors and peers. The state of Florida has established new standards for the Early Learning workforce and will provide some of the required training online. The authors have designed and developed an online professional development system that caters to this population, which ranges from low socioeconomic status workers to highly educated school directors. This population also includes non-native English speakers, non-English speakers, as well as native bilingual and monolingual English speakers. The diverse nature of the target population presented many challenges. The course content had to communicate sophisticated concepts such as communities of practice, cognitive development, and how to develop curriculum. The course content had to engage students who may not have graduated from High School, while at the same time, keeping the interest of more highly educated learners. The authors also sought to scaffold users into the use of sophisticated Information and Communications Technology, such as social media tools, an online portfolio, and synchronous online collaboration. Given these challenges, the authors looked to the principals of Universal Design for Learning and Learner Centered Design to develop a user-interface that is at once non-threatening and engaging. The authors started with the assumption that users should interact with a simple, intuitive interface that facilitates learning, communication and collaboration, while limiting distractions and potential frustration. As such, they developed a user interface layer to the popular open-source learning management system, Moodle that greatly reduces the number of user options and focuses user attention on immediate learning objectives. We took this approach in order to be able build upon the powerful features of Moodle, including teacher and administrative tools, while providing an interface to the learner that does not great effort to learn in and of itself. This UI consists of a simple windowed system that gives users linear access to content, learning activities, assignments and assessments, while at the same time allowing for interaction with instructors, course peers and professional colleagues. The latter is achieved by means of simple wiki tools, contextual micro-blogging, a synchronous "chat" feature and a direct interface to an online professional community of practice. Learners are gradually taught to use these tools by engaging in course learning activities that are designed to scaffold such outcomes. The purpose of this presentation is to share our experiences in developing an online professional development system with the greater online educational community. The system was developed using open source software, and in this spirit we hope our experiences will inform others who are confronted by similar challenges and goals. We hope to spend a significant part of the session engaging in discussion around the design of learning environments, approaches to the pedagogy of diverse populations, strategies for developing user-friendly interfaces, scaffolding technologically naive users, and the scalability and adoption of online learning systems for large populations.