This report deals with the question of obtaining insights into states of prior knowledge and exploring knowledge state tests and knowledge state profiles. The first part introduces a few basic terms important in the context of prior knowledge state. Evaluation and the validity, reliability, and usefulness of tests are considered in a prior knowledge context. "Value added" is discussed as students' gains on tests of knowledge and skill, a measurable indication of the effects of instruction. In the second part of the report, various knowledge state tests are discussed, and the results obtained in a domain-specific knowledge state test are reviewed. The domain-specific test was constructed from the economics test item bank at the University of Limburg (the Netherlands). Results of 536 first-year students were analyzed to obtain knowledge profiles that may be used to compare groups of students or to determine whether prior knowledge profiles of good and poor students differ. Further study will clarify whether prior knowledge state profiles can help in the determination of the effectiveness of educational efforts. Six figures illustrate the analysis. (Contains 47 references.) (SLD)