Does mixed physics homework improve later problem-solving?
Interleaved physics homework improved surprise-test performance despite feeling harder, but the study did not find significant gains on the subsequent high-stakes midterms.
Source
Interleaved practice enhances memory and problem-solving ability in undergraduate physics
Study at a glance
- Design
- Human experiment — Counterbalanced classroom intervention across two self-selected lecture sections
- N
- N=290 · 350 enrolled; 290 analysed in Stage 1 and 286 in Stage 2
- Population
- Undergraduate life-sciences students in introductory physics at UCLA
- Outcome
- Surprise-test formula recall and problem-solving; secondary midterm examination scores
- Comparison
- Interleaved versus blocked homework; sections switched schedules between stages
- Test delay
- Surprise tests in weeks 4 and 8; topic lags at least 1–3 weeks; midterms 3 days later
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Does mixed physics homework improve later problem-solving?
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Who participated and how large was the analysed sample?
Participants were 350 undergraduate students enrolled in either of two back-to-back lecture sections of Physics 5 C (“Physics for Life Sciences Majors: Electricity, Magnetism, and Modern Physics”) at the University of California, Los Angeles (UCLA) in Winter 2020, which began on 6 January 2020 and ended on 20 March 2020.
What was the main finding?
Interleaving yielded higher criterial test scores than blocking in Stage 1, d = 0.40, 95% CI [0.17, 0.65], t(288) = 3.41, p = 0.0008, and in Stage 2, d = 0.91, 95% CI [0.66, 1.20], t(284) = 7.68, p < 0.0001.
What they did
Two introductory university physics lecture sections used counterbalanced practice schedules over eight weeks. One section received blocked practice then interleaved practice; the other received the reverse. The analysis included 290 students in the first stage and 286 in the second, from 350 enrolled. Homework mixed topics or kept related problems together. Surprise tests at weeks four and eight required relevant formulas and solutions to novel problems.
What they found
Interleaving improved surprise-test scores in both stages, with effect sizes d = 0.40 and d = 0.91. Students more often recalled relevant formulas and produced fully correct answers, although the benefit was stronger for formula recall than exact solutions. Interleaved homework felt harder and yielded poorer homework performance. Scores on the high-stakes midterms three days later did not differ significantly between practice conditions.
The limits
What it doesn't show
Students chose lecture sections rather than being individually randomised. Interleaving also spaced topics and gave more recent practice for some material, so the mechanism is not isolated. The relevant surprise-test lags were at least one to three weeks, not a single identical delay. Later cramming and the surprise test itself may have reduced differences on midterms. The study does not establish that interleaving universally raises exam grades.
Key terms
- Retention interval
- The time between the last learning opportunity and the outcome test.
- Comparison condition
- The alternative study activity or exposure against which a result is assessed.
- Generalisation
- Whether a result applies to other populations, materials, settings or outcomes.
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Common questions
Does interleaving improve learning?
It improved surprise-test performance in this physics course, but the result depends on the task, comparison, and assessment.
Does it guarantee higher exam grades?
No. The high-stakes midterms did not show significant condition differences.
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