This website describes the Mathematics Problem-Solving Model developed by educators and researchers at the NW Regional Educational Laboratory's Mathematics and Science Education Center. The Model is intended to help educators "meet the challenges of teaching and assessing open-ended problem solving" by providing a scoring guide for problem solving, open-ended tasks, and examples of student work for practice in scoring. The website provides an overview of the components of the model, teaching strategies for mathematics problem solving, and other resources. Issues to consider in performance assessment and a discussion of some student work examples are included.