Effective school leadership is key to students' academic success. But the development of effective school leadership has been seriously hampered by the lack of technically sound tools to assess and monitor leaders' performance. With support from The Wallace Foundation, a team from Vanderbilt has been developing such an assessment system, and this paper presents the conceptual framework for their learning-centered tool. As described in this report, the Vanderbilt assessment system will contrast sharply with existing tools by focusing "100 percent" on topics related to instructional leadership and by clearly defining and measuring the leader behaviors that can improve learning. Unlike existing tools, it will also assess both individual leaders and leadership teams. Field testing is set for completion in 2008 and it will be widely available thereafter. Meanwhile, this paper previews the basics of this much-needed new assessment system. (Contains 2 figures.)