As a high school principal, the author came to realize that the traditional teacher observation and evaluation model did not help teachers become reflective and improve their practice. Because his own use of brief, frequent principal walk-throughs had given him valuable insights into the need for instructional improvements, he decided to offer veteran teachers the opportunity to forgo traditional classroom observations and instead to participate in the walk-through process with him. In this article, he describes how his school gradually implemented collaborative walk-throughs that enabled teachers in different subject areas to talk together about instruction and create a collaborative professional development culture.