This paper describes the process for creating and validating an assessment test that measures the effectiveness of instruction by probing how well that instruction causes students in a class to think like experts about specific areas of science. The design principles and process are laid out and it is shown how these align with professional standards that have been established for educational and psychological testing and the elements of assessment called for in a recent National Research Council study on assessment. The importance of student interviews for creating and validating the test is emphasized, and the appropriate interview procedures are presented. The relevance and use of standard psychometric statistical tests are discussed. Additionally, techniques for effective test administration are presented. (Contains 1 note and 2 figures.)