Steve Bloom, Associated Press
Sporting a colorful Dr. Seuss hat from the popular children's reading books Olympia View Elementary School principal Bob Richards plays a song request during the March 25, 2013 lunch period while perched on the school's roof above the playground in Lacey,Wash.

It’s logical to assume that school principals have an academic impact at their schools, but statistical proof is hard to come by. Many factors are at play in any school — teacher quality and students’ economic levels, to name but two of the main ones.

A new study published in Education Next journal uses a complex formula to isolate the effect of school principals on student achievement, and suggests that what was suspected is true: effective school principals do raise academic outcomes for students in their schools.

The study used a “value-added” method to measure how average gains in student achievement differed among principals. The formula included statistical adjustments for differences in school characteristics and students’ ethnicity and economic levels. To further determine a principal’s effectiveness, the study looked at how a principal’s performance compared to performance of other principals who led the same school, and how individual principals performed in different schools.

Results showed that highly effective principals raise achievement of a typical student by two to seven months of learning in a single school year and ineffective principals lower achievement by a similar amount. A disturbing finding was that principals who are least successful at raising student achievement don’t get weeded out of the labor market, especially in schools that serve disadvantaged students.

However, effective school principals make their greatest impact at elementary schools and in high-poverty, high-minority schools, said a Center for Public Education study.

Schools with effective principals have fewer student and teacher absences and are better at replacing poor teachers with effective ones. Their principals stay at least three years, the study showed.

The study said that the job of principal has changed from traditional administrative and building manager duties. Today's principal is an instructional leader who directs teacher development and student achievement. The best school principals have a clear sense of instructional goals and give ongoing feedback that supports those goals.

Effective principals are backed by school board leaders who understand what constitutes a good school and create a framework that gives principals autonomy and support in reaching goals, the study found.

School principals have five key responsibilities, a report for the Wallace Foundation found. Those include:

Shaping a vision of academic success for all students, one based on high standards.

Creating a climate of cooperation.

Cultivating leadership in others so that teachers and other adults assume their parts in realizing the school vision.

Improving instruction to enable teachers to teach at their best and students to learn to their utmost.

Managing people, data and processes to foster school improvement.

A different report from the Wallace Foundation identified ways to prepare and develop effective principals. It said that states and districts should provide better, more selective training for principals by using proven practices that include:

Selective recruitment practices to identify expert teachers with leadership potential.

A coherent training curriculum that focuses on instructional leadership, changing school culture and improving teacher skills.

Instruction that integrates problem-based learning, budget exercises, hiring principles and effective data use.

Administrative internships that provide real opportunities for aspiring principals to experience leadership firsthand.