While most pedagogical approaches to introductory level science seek to provide students with a conceptual understanding of important aspects of the subject matter, many typical assessment tools focus primarily on basic definitions and problems of an algorithmic character. Although this pedagogy has the sound foundation of stressing the "basics" (without which a conceptual understanding is impossible), it also has a weakness of which most faculty are also well aware. Namely, study methods such as rote memorization can often be used successfully (especially by the more capable students) to achieve good scores on exams while minimizing the time the student spends "wrestling" with the key concepts and the relationships among them. Thus, no matter how much the concepts might be stressed in lecture, students tend to focus on the "simplest" way to perform well on exams. The typical scenario is that only the strongest students tend to do well on the more conceptual or theoretical problems on exams, while the "weaker" students become confused because they can't see why their memorization-type strategies-which work so effectively for "most" of the problems-fail to work on the "hard" problems. Traditional curricula then rely on the fact that, eventually (perhaps, in the junior year), the conceptual intricacies of the subject matter finally crystallize, at least for those students who still are retained in the program.
By contrast, many innovative pedagogical methods, such as active and cooperative learning strategies, seek to engage students in activities that ensure that they do "wrestle" with the key ideas, and so (in theory) develop a stronger conceptual understanding, even at the freshman level. However, if this emphasis on concepts is not reflected in the grading and exam structure, these innovative learning strategies may have a minimal or even negative impact, precisely because students may believe that memorization-type strategies are what lead to acceptable exam scores. Thus, there arises the need for assessment tools that focus specifically on students' mastery and integration of key concepts. Such tools can be used both to obtain summative "snapshots" of students' conceptual understanding at, say, midterm or final exam time, as well as to assess the "delta effect" of a particular course/course component. To assess the delta (change) effect requires the use of a pre- "concept test" administered before students are exposed to the particular course/course component and then post- "concept testing" after exposure. Documenting whether a particular innovation has a positive impact on students' conceptual understanding is often used to determine whether the innovation was well implemented, or is whether it merits continued use.