The impact of having a great teacher is well-known. But what about school principals? Turns out that students learn more when their schools have principals who are part of a deliberate effort by their districts to ensure that they are well-prepared and well-supported.

That is the conclusion of a RAND study of a seven-year initiative supported by The Wallace Foundation.

“We found no other comprehensive district-wide initiatives with demonstrated positive effects of this magnitude on student achievement,” said Susan Gates, the lead researcher for RAND.

Principal Pipelines: A Feasible, Affordable, and Effective Way for Districts to Improve Schools was commissioned by The Wallace Foundation to evaluate an initiative it began started in 2011. Six large urban districts were selected to participate in its Principal Pipeline Initiative: Charlotte-Mecklenburg, Denver; Gwinnett County, Georgia; Hillsborough County, Florida; Prince George’s County, Maryland; and New York City.

Over the span of five years, the districts got together and developed standards, policies, and practices to clarify the pathway to the principalship in their districts. The pipelines include:

• identifying teachers as possible leaders
• supporting these teachers in getting their principal credential with a partner university or other principal preparation program
• hiring them and placing them in specific schools where their strengths were important — mostly high-need schools
• pairing them with well-prepared principal supervisors

Each of the six districts adapted the basic pattern of the pipeline to fit their own context, and detailed descriptions of each of the pipelines and how they work are available at the Wallace Foundation’s Knowledge Center, including a podcast sharing “Lessons from the Field” featuring practitioners from the districts.

Although the grant ran out in 2017, the districts have sustained and continued to refine their pipelines.

The RAND study found that the longer the pipeline was in place, the larger the effect. So, for example, in the second year of full implementation reading scores of schools with new principals who had been through the pipeline were, on average, 4.94 percentage points higher than matched schools. Similarly, in the third year of full implementation, the reading scores were on average 6.22 percentage points higher. The gains were more modest in math, but the effect was strongest among the schools that are the lowest performing. It was also strongest at the middle school level.

Five of the districts showed strong results in reading achievement and five had strong results in math achievement. Unfortunately, the results are not reported in a way that allows us to tell which of the district or districts did not show improvement.

However, the overall picture is clear: Districts that pay close attention to who leads their schools, how they are prepared, and how they are supported, should see gains in student achievement.

Since there has been relatively little time to show effects on student achievement, the implication is that as time goes on the effects will become stronger.

The RAND study is the first time a sustained initiative dedicated to improving the principal workforce has been demonstrated to have actual effects on student learning.

In a separate analysis commissioned by The Wallace Foundation, Abt Associates, found that the results were sufficiently robust as to meet the qualifications for evidence required under ESSA, the 2015 iteration of the Elementary and Secondary Education Act. This means that districts seeking to improve schools may use federal Title I money to build principal pipelines.

Overall, the costs of building a coherent pipeline to the principalship were modest, especially when the costs of principal turnover were taken into account. About one in five principals in high-need schools leaves every year and the average cost of replacing that principal is about $75,000. The RAND study demonstrated that principals who participated in the pipeline stayed in the job longer than those who were not part of the pipeline, making the whole cost of a pipeline initiative on average about $42 per student.

The bottom line: invest in school leadership, and student achievement will follow.