This document discusses diagnostic language assessment and lessons learned from rapid prototyping. It outlines the rationale and process for diagnostic language assessment, focusing on email writing. Rapid prototyping techniques are then described, from low to high fidelity prototypes using tools like Axure RP. Key lessons learned include the need for early user testing to identify requirements, using prototypes to find usability issues before full development, and prototypes serving as an interactive communication aid between stakeholders.