According to two major school districts currently involved in this very debate, the answer isn't terribly clear. (publicschoolreview.com)
This study by the Council of the Great City Schools explores ways in which principal supervisors are selected, supported and evaluated in major school districts in the U.S.. (wallacefoundation.org)
He found that Chicago students were improving faster than students in any other major school district in the country. (cepa.stanford.edu)