It's jargon, and in this case “knowledge decay” refers to how fast students forget what they have learned for a test. There's a general sense among faculty that they forget a lot, quickly. Research would respond to our general impressions with answers that clearly support “it depends” conclusions. A study done in a chemistry class illustrates this. The research team started with the big general question. Does knowledge decay occur in chemistry courses? And if it does, when? The study answered these questions with data collected in three different courses: an undergraduate chemistry course for nursing students, another for nonscience undergraduates, and another for high school honors students.
It's jargon, and in this case “knowledge decay” refers to how fast students forget what they have learned for a test. There's a general sense among faculty that they forget a lot, quickly. Research would respond to our general impressions with answers that clearly support “it depends” conclusions. A study done in a chemistry class illustrates this. The research team started with the big general question. Does knowledge decay occur in chemistry courses? And if it does, when? The study answered these questions with data collected in three different courses: an undergraduate chemistry course for nursing students, another for nonscience undergraduates, and another for high school honors students. As would be expected, these course exams contained different content, but all of them included “open-ended, course-specific, conceptual, and skill questions” and were administered at approximately one-month intervals (Bunce, VandenPlas, & Soulis 2011, p. 1233). Following each exam, students took quizzes that repeated a subset of the test questions at one of three time intervals: two-to-five days after the exam, six-nine days after, and 10–17 days after. Each student took one of the quizzes at one of the time intervals, and the interval was randomly selected.
They found that “students enrolled in courses in which the continued spiral use of chemistry concepts is not evident, frequent quizzing opportunities are not provided, and a final exam is not given experience a significant decrease in achievement during the first 48 h following a test” (p. 1231). The continued spiral use of the content refers to curricula in which students get course content on a need-to-know basis. The concepts are revisited several times during the chapter and across several chapters with more detail provided in each encounter. Moreover, the amount of knowledge lost in these courses was stable. After the initial decay, it did not decline further.
Beyond this general conclusion are details that show how context affects educational outcomes. For students in two of these courses (nursing and high school honors chemistry), knowledge decay did not occur. The researchers' first supposition was that these student cohorts were motivated. Nursing students have exams they have to pass to be licensed, and honors students are motivated to achieve good grades for college admission, but nonscience majors don't have those motivations in chemistry courses. However, when the research team analyzed the motivation data collected on nonscience majors, the results did not justify concluding that a lack of motivation was the reason the nonscience majors experienced knowledge decay.
What was different about the course for nonscience majors was the absence of quizzes between major exams and no cumulative final exam. The nursing students had daily quizzes. The high school students had some additional quizzing but were also required to regularly submit homework, which was graded. Students in both of these courses took cumulative finals. What appeared to prevent knowledge decay in this study would not surprise those in cognitive psychology, whose work has repeatedly demonstrated the value of retrieval practice. New knowledge is remembered better and longer the more often it is retrieved. Students need to review regularly. They need to face questions (on quizzes and in homework) that cause them to recall what they have recently learned. The connections between what they already knew and what they've just learned need to be cemented, and when that new information is integrated with the old, it becomes part of a learner's working knowledge base.
Beyond this further confirmation of the value of repeated exposure to content are larger implications that pertain to the tendency of many faculty to accept widely held assumptions. It may well be that in a particular course, given the content, how it is taught, and the students enrolled in the course, significant amounts of knowledge decay occur that can be pegged to motivational issues. But that conclusion should not be taken as fact without further analysis. Motivation is frequently a problem in required courses not in the students' major, but it wasn't the problem in this chemistry course and wasn't the most likely reason for the knowledge decay.
We continue to want simple, generalizable answers to questions that appear straightforward. As these researchers note, their work addresses the first in a set of questions. Does knowledge decay occur, and does it occur quickly? As is invariably the case, their answers offer insight and lead to more questions. “Future studies could investigate the causes of decay of knowledge in a more systematic fashion” (p. 1236). They think the causes may include the presence or absence of repeated occasions of tests and quizzes, student ability, student motivation, teaching style, interactive versus passive classrooms, and the use of cumulative finals, among others. It's not a straightforward question with a simple answer.
Reference: Bunce, D. M., VandenPlas, J. R., & Soulis, C. (2011). Decay of student knowledge in chemistry. Journal of Chemical Education, 88, 1231–1237.