There is widespread acknowledgement that the production of effective teaching and teachers is perhaps the critical component of education reform and innovation for improvement of student learning. This aim requires a serious investment of time, rigor, and evaluation to produce professional-development programs that actually work. This report illustrates features of new evidence-supported approaches to professional development that have promise for closing not only the evidence gap, but the achievement gap as well. The focus is on one web-based, scalable approach to professional development--MyTeachingPartner, or MTP--that illustrates how evidence-driven professional development can be designed and used to improve teacher effectiveness and student learning. MTP uses a standardized method of online, individualized coaching and a library of highly focused video clips showing effective teachers in action that are tightly coupled with a standardized metric for observing teacher practice in the classroom, called the Classroom Assessment Scoring System, or CLASS. This report provides background information on the broader challenges of building effective professional development for teachers, the theory of action that undergirds the CLASS-MTP system, and a description of the CLASS-MTP tools and evidence base. The report closes with a discussion of the policy and practice challenges of implementing effective systems of teacher professional development on a district or statewide level based on the evidence gleaned and lessons learned from this work. (Contains 2 figures, 1 table, and 27 endnotes.) [Preparation of this paper was supported in part by the Eunice K. Shriver National Institute for Child Health and Human Development.]