Formative assessment is intended to aid student learning, rather than to evaluate the student for purpose of selection or prediction of performance. The DIAGNOSER project has designed formative assessments using computer- presentations. The idea behind the DIAGNOSER, FACET-BASED INSTRUCTION, is that students come to a topic with pre-formed ideas. The goal of assessment is to identify these ideas and provide feedback tailored to the student’s current ideas, rather than just responding by telling the student that the answer was right or wrong. This method of assessment represents the student as being at a location in a space of knowledge states, rather than representing the student by a vector of factor scores. DIAGNOSER modules have been developed for topics in the physical sciences and in statistics, and have proven quite successful. DIAGNOSER modules are now being placed on the World Wide Web and are being coordinated with a program of high-stakes testing.