This article discusses how teaching via problem solving helps enact the Mathematics Teaching Practices and supports students' learning and development of the Standards for Mathematical Practice. This approach involves selecting and implementing mathematical tasks that serve as vehicles for meeting the learning goals for the lesson. For the lesson discussed in this article, the learning goals are developing students' understanding of number theory concepts (factors; multiples; greatest common factor, or GCF; and least common multiple, or LCM). The authors seek to continue a yearlong goal of developing students' problem-solving skills.