We have designed model-development sequences using a common context to provide authentic problem-solving experiences for first-year students. The model-development sequence takes a model-eliciting activity a step further by engaging students in the exploration and adaptation of a mathematical model (e.g., procedure, algorithm, method) for solving a problem for a realistic client. Here we describe an entire model-development sequence in which first-year engineering students are asked to develop, explore, and adapt a model for quantifying the size of aluminum crystals using digital images in response to the needs of an aluminum manufacturer. The intent of this paper is to highlight, by example, the components and educational value of a model-development sequence. [For "Quantifying Aluminum Crystal Size Part 1: The Model-Eliciting Activity," see EJ1063793.]