Teachers, unions, schools, and districts all seem to agree on the importance of teacher learning. The United States spends an estimated $18 billion on professional development programs every year, and teachers spend more than a week’s worth of time participating in them. From training seminars to coaching and small-group study, professional development is a major investment of money and time. But research shows that most of these efforts do not achieve substantial positive impacts on teacher performance or student outcomes. Studies also reveal a broad gap between the short-term, isolated experiences that typify professional development and the ongoing, content-focused, job-embedded professional learning that can help teachers and their students excel. Most professional development takes the form of a workshop that may not be relevant to every teacher who attends. Even when learning is focused on a particular content area, it tends to be short-lived, with most teachers participating in less than 16 hours of activities — on the order of a seminar or two in a year.