Looking for a good principal? Start your search with good teachers. That simple takeaway comes courtesy of a CALDER research paper, which finds that a teacher's 'value add' (measurable improvement in student learning) is predictive of principal value add in terms of learning gains across the school. In other words, more effective teachers make more effective principals.
What seems like common sense does not appear to be common practice. Reviewing the research literature on principal hiring practices, the researchers note that there is little evidence that teacher effectiveness is considered when hiring a principal.
An additional factor when selecting a new school leader is that teachers who become principals within the same school tend to be less effective. Running contrary to the expectation that direct school experience enhances effectiveness, greater gains are made by principals hired either from elsewhere in the district or externally.
One possible explanation for decreased effectiveness of within-school hires is the challenge of managing former peers. Another explanation is that familiarity with internal candidates is given outsized weight in the selection process, resulting in hiring individuals with lower qualifications.