Most (especially early) experimental literature on the spacing effect involves inauthentic learning environments

In particular, students are generally studying materials which are unrelated to their primary classroom focus—e.g. vocabulary words for languages they’re not learning; arbitrary facts about various animal species or places or historical events; etc.

It’s not clear to what extent results established in this context will extend to naturalistic settings.

An important early paper establishing the Spacing effect was Spitzer, H. F. (1939). Studies in retention. Journal of Educational Psychology, 30(9), 641–656; in this paper students study unrelated materials.

This is fairly typical for the literature: roughly speaking, I’d say about 80% of the papers I read are of this kind (or are in a laboratory setting rather than a classroom setting and so are even more inauthentic).

Over time, a small number of studies have interceded directly in a course’s curriculum and tested the Spacing effect (and often also the Testing effect) in that context. These studies are probably more instructive w.r.t. implications of these effects on Knowledge work. See e.g. systematic review Agarwal, P. K., Nunes, L. D., & Blunt, J. R. (2021). Retrieval Practice Consistently Benefits Student Learning: A Systematic Review of Applied Research in Schools and Classrooms. Educational Psychology Review..

Reading queue

Collecting papers to read about undergraduates or adult learners (drawn from Agarwal, P. K., Nunes, L. D., & Blunt, J. R. (2021). Retrieval Practice Consistently Benefits Student Learning: A Systematic Review of Applied Research in Schools and Classrooms. Educational Psychology Review.):

  • *Ayyub, A., & Mahboob, U. (2017). Effectiveness of test-enhanced learning (TEL) in lectures for undergraduate medical students. Pakistan Journal of Medical Sciences, 33, 1339.
  • *Atabek Yigit, E., Balkan Kiyici, F., & Çetinkaya, G. (2014). Evaluating the testing effect in the classroom: an effective way to retrieve learned information. Eurasian Journal of Educational Research, 54, 99–116.
  • Batsell, W. R., Perry, J. L., Hanley, E., & Hostetter, A. B. (2017). Ecological validity of the testing effect: the use of daily quizzes in introductory psychology. Teaching of Psychology, 44, 18–23.
  • *Bekkink, M. O., Donders, R., van Muijen, G. N., & Ruiter, D. J. (2012). Challenging medical students with an interim assessment: a positive effect on formal examination score in a randomized controlled study. Advances in Health Sciences Education, 17, 27–37.
  • Dobson, J. L., & Linderholm, T. (2015a). The effect of selected “desirable difficulties” on the ability to recall anatomy information. Anatomical Sciences Education, 8, 395–403.
  • Dobson, J. L., & Linderholm, T. (2015b). Self-testing promotes superior retention of anatomy and physiology information. Advances in Health Sciences Education, 20, 149–161.
  • Dobson, J. L., Perez, J., & Linderholm, T. (2017). Distributed retrieval practice promotes superior recall of anatomy information. Anatomical Sciences Education, 10, 339–347.
  • Foss, D. J., & Pirozzolo, J. W. (2017). Four semesters investigating frequency of testing, the testing effect, and transfer of training. Journal of Educational Psychology, 109, 1067.
  • Freda, N. M., & Lipp, M. J. (2016). Test-enhanced learning in competence-based predoctoral orthodontics: a four-year study. Journal of Dental Education, 80, 348–354.
  • Khanna, M. M., & Cortese, M. J. (2016). The benefits of quizzing in content-focused versus skills-focused courses. Scholarship of Teaching and Learning in Psychology, 2, 87, 1.
  • Kromann, C. B., Jensen, M. L., & Ringsted, C. (2009). The effect of testing on skills learning. Medical Education, 43, 21–27.
  • Kromann, C. B., Bohnstedt, C., Jensen, M. L., & Ringsted, C. (2010). The testing effect on skills learning might
    last 6 months. Advances in Health Sciences Education, 15, 395–401.
  • Kromann, C. B., Jensen, M. L., & Ringsted, C. (2011). Test-enhanced learning may be a gender-related phenomenon explained by changes in cortisol level. Medical Education, 45, 192–199.
  • Larsen, D. P., Butler, A. C., & Roediger, H. L. (2009). Repeated testing improves long-term retention relative to repeated study: a randomised controlled trial. Medical Education, 43, 12 1174–1181.
  • Larsen, D. P., Butler, A. C., & Roediger, H. L. (2013a). Comparative effects of test-enhanced learning and self-
    explanation on long-term retention. Medical Education, 47, 7 674–682.
  • Larsen, D. P., Butler, A. C., Lawson, A. L., & Roediger, H. L. (2013b). The importance of seeing the patient:
    test-enhanced learning with standardized patients and written tests improves clinical application of knowl-edge. Advances in Health Sciences Education, 18, 3, 409–425.
  • Son, J. Y., & Rivas, M. J. (2016). Designing clicker questions to stimulate transfer. Scholarship of Teaching and Learning in Psychology, 2, 3, 193–207.