This paper measures effective leadership preparation and assesses its relationship to what principals learn about leadership, their leadership practices, and school improvement progress and improved school climate (particularly for academic press and continuous improvement). This paper draws on survey research conducted in 2005 with 125 principals who had graduated from one of four exemplary leadership preparation programs documented through a Stanford University study founded by the Wallace Foundation (Darling-Hammond, Meyerson, LaPointe, & Orr, 2007), and a national comparison sample of 571 principals. Correlation results show moderate to strong relationships among study measures. Through a series of multiple regressions, the study shows the moderating influence of leadership preparation on schools' improvement progress and effective school climate (for academic press and continuous improvement) through how frequently principals performed instruction leading work (such as working with teachers on their instruction). School context [poverty (positively) and the extent of challenging problems(negatively)] has a mediating influence on the leadership practice-school improvement progress-effective school climate relationships. Appended are: (1) Programs Sampled; (2) Scales' items, statistics and factor loadings; and (3) Skewness and kurtosis of primary measures. (Contains 2 figures, 19 tables and 1 footnote.) [This paper was commissioned by The Wallace Foundation. For the main report, "Preparing School Leaders for a Changing World: Lessons from Exemplary Leadership Development Programs. School Leadership Study. Final Report," see ED533003.]