With research indicating substantial differences among teachers in terms of their effectiveness (Nye, Konstantopoulous, & Hedges, 2004), a major focus of recent research in education has been on improving teacher quality through professional development (Desimone, 2009; Institute of Educations Sciences [IES], 2012; Measures of Effective Teaching project [MET], 2012; Wayne, Yoon, Zhu, Cronen, & Garet, 2008). Notwithstanding widespread support for the development of teachers, there is a growing recognition of the lack of reliable empirical evidence concerning which features and programs of professional development are effective (Wayne et al., 2008). Consequently, there has been strong interest in supporting research that can inform the design of effective professional development programs (Desimone, 2009; IES, 2012; Wayne et al., 2008; Garet et al., 2011). For instance, through many different programs and topics, the Institute of Education Sciences (IES) has funded dozens of projects that targeted the professional development of teachers and has recently established an entire program devoted to research on effective strategies for improving teacher quality through professional development (IES, 2012). Despite the national emphasis on improving teacher effectiveness and development, there has been little research discussing how to effectively design and implement teacher professional development studies (Wayne et al., 2008). Perhaps because of this lack of research, examples of professional development studies with high quality designs have been rare. For these reasons, the field has called for more studies that evaluate the effectiveness of professional development programs on valued outcomes using rigorous designs (Barrett et al., 2012). In this study, the authors empirically examined the comparative power and practical viability of several different types of cluster randomized trials in professional development studies. They outline why such designs are well suited for studies of many professional development programs. They then report estimates for parameters needed to plan such studies and use the estimates to explore the comparative efficiency of several designs. Tables are appended.