Model-eliciting activities are based on real-life situations where students, working in small groups, present a mathematical model as a solution to a client's need (Zawojewski & Carmona, 2001). The problem design enables students to evaluate their solutions according to the needs of a client identified in the problem situation and sustain themselves in productive, progressively effective cycles of conceptualizing and problem solving. Model-eliciting activities (MEAs) are ideally structured to help students build their real-world sense of problem solving towards increasingly powerful mathematical constructs. What is especially useful for mathematics educators and researchers is the capacity of MEAs to make students' thinking visible through their models and modeling cycles. Teachers do not prompt the use of particular mathematical concepts or their representational counterparts when presenting the problems. Instead, they choose activities that maximize the potential for students to develop the concepts that are the focal point in the curriculum by building on their early and intuitive ideas. The mathematical models emerge from the students' interactions with the problem situation and learning is assessed via these emergent behaviors.