The National Council of Teachers of Mathematics (NCTM, 2014) highlights that effective teaching practices promote students' reasoning and sense making through various problem-solving strategies. Rather than telling students what to do and how to solve problems, teachers are expected to engage learners in accessible real-life problem situations that lead them through a process of choosing and using appropriate quantities, engaging in sense making of quantitative relationships developing mathematical models, and analyzing those models to refine decisions in problem contexts. This article offers three instructional phases a high school teacher, Ms. A, used to facilitate a lesson that positions students' quantitative reasoning as the central mechanism of problem solving to determine the most reasonable solution in the problem context. It reveals how her students created and modified mathematical models using quantities and then interpreted their results while addressing the question of fairness and reasonableness. Her lesson phases reflect a balance between listening to the students' discoveries and addressing the instructional goals for the lesson. The problem, using the coordinate system, asks students to develop a system for ranking soccer teams. The absence of labels for the axes requires students to reason about the relative quantities at the labeled points and determine the scales of the axes.