The process of method development is at the heart of analytical chemistry, yet direct experimental experience with the process is rarely taught in the undergraduate laboratory. We report here an experiment that uses rapid, safe, and inexpensive paper-based microfluidics with cell phone detection in order to facilitate the development of a colorimetric method for the determination of iron with three different derivatizing agents (thiocyanate, 1,10 phenanthroline, or FerroZine). This lab has been developed with an inquiry-based pedagogy where students determine which figures of merit to measure, the order to measure them in, and their own procedures for measuring them. This experiment gives students the opportunity to measure linear range, sensitivity, selectivity, accuracy, precision, limit of detection, and optimal reaction time for each derivatizing agent. Students then compare and contrast the measured figures of merit to make an evaluation of which method is preferred for iron quantitation. The results are variable enough from group to group, and each derivatizing agent has different advantages and disadvantages so that there is no "right" answer. This experiment is very flexible and can be modified to fit into one or two lab periods, be delivered with students working in groups or individually, and be delivered in person or in a remote setting. Student learning was assessed using the Enhancing Learning by Improving Process Skills in STEM (ELIPSS) rubrics for management, critical thinking, and information processing. Students demonstrated growth in many skills and expressed significant appreciation for their own learning.