A Year of Desirable Difficulties: The Impact of Interleaving Math Practice in Nigeriahttps://doi.org/10.7910/DVN/BBS0SHGray-Lobe, GuthrieHarvard Dataverse2026-03-312026-03-31T20:28:35ZThis paper tests whether increasing students’ exposure to “desirable difficulties” improves learning in real classrooms. In a year-long field experiment in Nigerian primary schools, interleaved math practice raised short-term test performance by 0.28 standard deviations but had no effect on cumulative end-of-year assessments. Gains were concentrated among lower-achieving students, while higher-achieving students saw little or no benefit. The results suggest that strategies that make learning more effortful can boost short-term mastery but may not produce durable improvements, highlighting the limits of applying laboratory-based cognitive interventions at scale.Social SciencesMichael Kremer, Guthrie Gray-Lobe, Joost de Laat, and Lotte van der Haar, "A Year of Desirable Difficulties: The Impact of Interleaving Math Practice in Nigeria," NBER Working Paper 31853 (2023), https://doi.org/10.3386/w31853., url, https://www.nber.org/papers/w318532026-03-31Gray-Lobe, Guthrie2026-03-23CC0 1.0