SALT LAKE CITY — School principals do a lot more than strike dread in the hearts of misbehaving kids, even if that’s how many people remember them.

A new study published in the Education Next journal gives statistical proof that effective principals raise academic achievement of students at their schools.

The most effective principals raise achievement of a typical student by two to seven months of learning in a single school year, according to the "School Leaders Matter" study. The least effective principals lower achievement by a similar amount. Seven thousand principals were studied, using data from the Texas Education Agency going back to 1993.

Researchers adjusted for the fact that a principal in a school that serves mostly wealthy families might appear to be doing a great job, when students' high achievement was really driven by family background factors.

The statistical adjustments also leveled the field for principals working with disadvantaged students whose achievement scores were comparatively low. Such a principal could be producing better student achievement results than other principals did in similar circumstances. A statistical process known as value-added measurement was used to tease out that information.

Honing in

A principal new to a school inherits a particular group of circumstances that influences ability to improve achievement. That's another reason that it's difficult to isolate the impact a school principal makes, said Steven Rivkin, a co-author of the study.

"A principal enters a school, and the vast majority of teachers were there before. The curriculum is there, and the school is under district rules and state rules," Rivkin said. "One of the hard things we are trying to do is look at patterns in the data that really confirm that we are actually capturing principal effects."

The study factored in how each principal’s performance compared to performance of other principals who led the same school, and how individual principals performed in different schools over their careers. And the calculations included measures of teacher effectiveness based on value-added evaluations of teacher quality.

After all data was considered, scores for the 7,000 principals in the study were arranged on a distribution scale. This allowed researchers to determine which principals were most and least effective at raising student achievement, and led to several other conclusions.

Principal turnover

Besides showing that student achievement rises when an effective principal is at a school's helm, the study showed principal turnover is much higher in schools that serve disadvantaged populations. That's significant, because it takes time for effective principals to have a positive impact on student success.

"Unlike teachers, who can go in and directly impact students, principals do it indirectly," said James Hull, senior policy analyst for the Center for Public Education. "They do it through the quality of teachers they retain and bring in, and the support they provide for them. That doesn't happen overnight. Optimally, it takes five to seven years."

Hull authored a 2012 study that found that high principal turnover had an adverse impact on schools, felt most keenly at the most challenging schools.

"For many principals, their first job is at a challenging school," Hull said. "They get their experience, and after two or three years they move on to less challenging and more prestigious jobs in their districts — easier jobs that pay just as much."

Hallmarks of quality

Hull's study drew conclusions about hallmarks of effective school principals. The best of them are true instructional leaders who set the tone for school curriculum and teacher development, he said. Meanwhile, they retain their traditional administrative duties, which include setting the tone for student discipline.

"Good principals help teachers improve instruction," Hull said. "They identify those that have high skills and make sure they retain them. Those teachers that don't have good skills, they are able to replace with teachers who have greater skills. They are good motivational leaders who create an environment where students and teachers enjoy coming to school."

Hull said there is no "silver bullet" for solving high principal turnover, but several recommendations arise from current research.

"First, we have to identify highly effective principals," he said, adding that sophisticated value-added measurements like those used in the "School Leaders Matter" study should be part of a broader process for doing that. Rivkin, too, believes value-added evaluations are only a partial measure of principal effectiveness.

"Districts have to be very careful not to over-rely on value-added estimates as their sole measures of principal or teacher performance," he cautioned. "They provide one piece of information that should be used in combination with personal observation, a standard tool in virtually all occupations and industries."

Both researchers recommend that school districts create incentives for keeping excellent principals in one school long enough for them to make a positive impact.

That can be done through higher salaries, better working conditions and more support for principals who remain at the most challenging schools, Hull said.