States and districts facing pressure to have all children meet high standards have been paying overdue attention to improving school leadership as a way to advance instruction and drive needed changes throughout schools. What will it take to ensure that "all" public schools have leaders equal to the challenges facing them? That question has placed fresh urgency on addressing the chronic weaknesses of principal training programs, criticized for decades as unselective in their admissions, academically weak and poorly connected to school realities. Armed for the first time with compelling, research-validated examples of effective practices, more districts--especially large urban districts with the most acute needs--have been investing in raising the quality of pre-service training and providing more rigorous mentoring and other support to newly hired principals. And more states have been taking steps including tightening accreditation rules and adopting new standards to push universities and other training providers to improve their programs. Some districts, such as Chicago and Denver, have collaborated with willing universities to design better training for aspiring principals. Others, such as New York City, Boston and Gwinnett County, Ga., have formed their own training academies or are working with non-profit training providers to create programs suited to their needs. It's too soon to say for sure, but early evidence suggests payoffs for schools might include lower principal turnover and higher student performance. While these signs of heightened attention are encouraging, there is still a long way to go before the majority of the nation's aspiring principals get the training they need to succeed. Experience and new research suggest that heeding the following five lessons could help propel many more districts toward the goal of having strong leadership in every school: (1) A more selective, probing process for choosing candidates for training is the essential first step in creating a more capable and diverse corps of future principals; (2) Aspiring principals need pre-service training that prepares them to lead improved instruction and school change, not just manage buildings; (3) Districts should do more to exercise their power to raise the quality of principal training, so that graduates better meet their needs; (4) States could make better use of their power to influence the quality of leadership training through standard-setting, program accreditation, principal certification and financial support for highly qualified candidates; and (5) Especially in their first years on the job, principals need high-quality mentoring and professional development tailored to individual and district needs. (Contains 64 footnotes.)