I’ve been following the spacing effect for over a decade, writing a research-to-practice report in 2006, and recommending the spacing effects to my clients and in the guise of subscription learning (threaded microlearning).

One of the fascinating things is that researchers continue to be fascinated with the spacing effect producing about 10 new studies every year and many research reviews.

Here are a list of the research reviews from most recent to earliest.

• Maddox, G. B. (2016). Understanding the underlying mechanism of the spacing effect in verbal learning: A case for encoding variability and study-phase retrieval. Journal of Cognitive Psychology, 28(6), 684-706.
• Vlach, H. A. (2014). The spacing effect in children’s generalization of knowledge: Allowing children time to forget promotes their ability to learn. Child Development Perspectives, 8(3), 163-168.
• Küpper-Tetzel, C. E. (2014). Understanding the distributed practice effect: Strong effects on weak theoretical grounds. Zeitschrift für Psychologie, 222(2), 71-81.
• Carpenter, S. K. (2014). Spacing and interleaving of study and practice. In V. A. Benassi, C. E. Overson, & C. M. Hakala (Eds.), Applying science of learning in education: Infusing psychological science into the curriculum (pp. 131-141). Washington, DC: Society for the Teaching of Psychology.
• Toppino, T. C., & Gerbier, E. (2014). About practice: Repetition, spacing, and abstraction. In B. H. Ross (Ed.), The psychology of learning and motivation: Vol. 60. The psychology of learning and motivation (pp. 113-189). San Diego, CA: Elsevier Academic Press.
• Carpenter, S. K., Cepeda, N. J., Rohrer, D., Kang, S. H. K., & Pashler, H. (2012). Using spacing to enhance diverse forms of learning: Review of recent research and implications for instruction. Educational Psychology Review, 24(3), 369-378.
• Kornmeier, J., & Sosic-Vasic, Z. (2012). Parallels between spacing effects during behavioral and cellular learning. Frontiers in Human Neuroscience, 6, Article ID 203.
• Delaney, P. F., Verkoeijen, P. P. J. L., & Spirgel, A. (2010). Spacing and testing effects: A deeply critical, lengthy, and at times discursive review of the literature. In B. H. Ross (Ed.), The psychology of learning and motivation: Vol. 53. The psychology of learning and motivation: Advances in research and theory (pp. 63-147).
• Cepeda, N. J., Pashler, H., Vul, E., Wixted, J. T., & Rohrer, D. (2006). Distributed practice in verbal recall tasks: A review and quantitative synthesis. Psychological Bulletin, 132(3), 354-380.
• Janiszewski, C., Noel, H., & Sawyer, A. G. (2003). A Meta-analysis of the Spacing Effect in Verbal Learning: Implications for Research on Advertising Repetition and Consumer Memory. Journal of Consumer Research, 30(1), 138-149.
• Dempster, F. N., & Farris, R. (1990). The spacing effect: Research and practice. Journal of Research & Development in Education, 23(2), 97-101.
• Underwood, B. J. (1961). Ten years of massed practice on distributed practice. Psychological Review, 68(4), 229-247.
• Ruch, T. C. (1928). Factors influencing the relative economy of massed and distributed practice in learning. Psychological Review, 35(1), 19-45.