“Moderate positive evidence” — Education Endowment Foundation
The EEF identified 12 interleaving studies involving learners aged about 8–14. Eleven concerned mathematics, and the review judged the evidence moderately positive for helping Key Stage 2 and Key Stage 3 pupils select appropriate solutions to maths problems. The evidence was concentrated in controlled materials and strategy selection, so it does not establish a fixed GCSE or A-level grade gain.
A large US Grade 7 trial involved 787 students in 54 classes. One month later, the interleaved group averaged 61% on a researcher-created test, compared with 38% for the blocked group. The What Works Clearinghouse judged the study to meet its standards without reservations. Those percentages illustrate a delayed-learning effect in one setting; they are not a prediction for an individual UK student or public examination.
A 2019 meta-analysis found an average benefit but substantial variation by material: visual categories and mathematical tasks were more favourable, while word materials favoured blocking on average. A 2021 systematic review also found benefits for concept recognition and transfer, but much of the literature involved laboratory tasks, university students, visual examples or short materials.
Interleaved work can therefore feel less fluent during practice without being less valuable later. That does not make every low score productive: if you cannot start, repeatedly guess or cannot use the correction, reduce the difficulty and rebuild the foundation.
