The current reform movement in mathematics education urges teachers to support students as they make sense of mathematics, while also ensuring that they gain specific mathematical skills and knowledge. The tension between these two expectations gives rise to what we call the dilemma of telling: how to ensure that students come to certain mathematical understandings, without directly telling them what they need to know or do. Our study focused on how two middle school mathematics teachers who were incorporating many aspects of reform mathematics into their instruction responded to this dilemma. Data sources include classroom observations and videotapes of lessons over a three-year period. We found that both teachers devoted the majority of class time to student conversations, both small group and whole class; however, the teachers strategically entered the student-dominated conversations by "telling" to meet specific curricular goals.