Conventional education wisdom dictates that one of a principal's main duties is to be an instructional leader. A new study looks at what this term really means and whether a principal's instructional leadership yields any benefit to students' academic achievement.

Jason A. Grissom and Susanna Loeb found that understanding instructional leadership was akin to opening up a Russian nesting doll - each finding encompassed a more nuanced finding hidden within it.

Layer 1: Overall, spending more time on instructional leadership doesn't make a difference for student learning.

Layer 2: The type of instructional leadership matters. At least in math, coaching teachers and evaluating teachers or curricula are associated with greater student achievement. However, spending more time on classroom walkthroughs is associated with a decrease in student achievement. These different outcomes help explain why instructional leadership overall is a wash.

Layer 3: The purpose for classroom walkthroughs matters. Walkthroughs intended to increase principals' visibility were counterproductive, while walkthroughs used for professional development - to identify areas where teachers may need additional support - were beneficial.

Layer 4: Pairing coaching with walkthroughs for professional development makes these practices even more effective.

Layer 5: All of these practices may tell us more than just how principals spent their time on one particular day - they may be proxies for the principal's general priorities and capacity to give teachers meaningful support and feedback.

Principals who considers themselves instructional leaders should consider whether their actions actually support teacher development and student achievement. And for the research community, it reminds us that the easy answers we glean from data may not always be the right ones - sometimes we need to dig a little deeper to find out what's really going on.