This large scale, research and technical assistance project investigates the nature of elementary and middle school principals' knowledge of mathematics and beliefs about mathematics teaching and learning through the construct of Leadership Content Knowledge (LCK) and its effect on their practices of classroom observation and teacher supervision. The project addresses the key MSP features of teacher retention, challenging courses and curricula and sustainability. All interested MSPs that address middle school mathematics will have the opportunity to participate. Phase I of the work yields diagnostic information about the principals' level of LCK which MSPs can use as a needs assessment. In Phase II half of the participants will receive leadership training in mathematics teaching and learning as an intervention to explore aspects of LCK that change most readily and those that are more resistant to change. Phase III will use comparative case studies to address how principals with known LCK conduct classroom observations, make judgments about the quality of instruction, and indirectly, affect students' mathematics achievement. The research allows the PI to refine instruments that assess the multidimensional aspects of LCK that will be shared through the MSP Learning Network.