81,000 assistant principals work in U.S. schools Over the last 25 years, the prevalence of U.S. schools with assistant principals has grown from one-third to one-half, but those leaders tend to be underused and underresearched, according to a report sponsored by the Wallace Foundation. The report finds that the assistant principalship appears to be an increasingly common stepping-stone to the principalship — about three-quarters of principals have served as assistant principals compared with about half 25 years ago — but there was no evidence that experience in the former role improves performance in the latter. That may be partly explained by a finding that assistant principals’ roles and responsibilities are very diverse and often poorly defined. The report finds untapped potential and room for improvement