Whole-group classroom discussions about solutions allow teachers to promote reasoning that moves students beyond merely noticing mathematical ideas toward developing a well-connected knowledge of concepts. Creating classroom environments where teachers promote reasoning and engage students in investigating important mathematical phenomena is critical for teaching math for understanding (Ball and Bass 2003; Kline 2008; NCTM 2000; Martin and Kasmer 2009). Nevertheless, many researchers have found that such discussions are challenging for teachers to facilitate in terms of establishing appropriate expectations for participation (Yackel and Cobb 1996), recognizing which aspects of the math to focus on (Ball, Hill, and Bass 2005), and deciding what kind of support to provide for students (Cengiz, Kline, and Grant 2011). This article presents vignettes from second-, third-, and fourth-grade classrooms to illustrate the complexity of the work of pursuing student reasoning. The author also offers suggestions for creating opportunities to promote reasoning. (Contains 2 figures.)