From a cognitive viewpoint, the students had all interred the material into their long term memory when it had been first presented. But to be able to test well on the material, it has to be moved into short term memory for immediate access. Without an intuitive understanding of that material however, that move from long to short is difficult. The more a student truly understand their course material, the easier it is for it to move into short term memory.
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| Figure 1: Short Term Memory at a certain time, (t). |
After the exam, all of that material is generally leaked slowly out of short term memory unless it is periodically used to keep it immediate. However, once in short term memory implies that it is possible to reinter the material back into short term even if it had been leaked out. Hence, it is fine for students to 'forget' their material after an exam. Since now, it will be possible if necessary, for a student to recall that material with ease.
One reference appoints the above notions as Long Term Memory (LTM) and Working Memory (WM) instead of Short-Term Memory. In that study, their results indicate that LTM and WM are indeed distinct but related constructs [1].
References:
[1] Nash Unsworth. On the division of working memory and long-term memory and their relation to intelligence: A latent variable approach. Acta Psychologica, 2010. Available at http://maidlab.uoregon.edu/PDFs/Unsworth(2010)Acta.pdf.
