A Year of Desirable Difficulties: The Impact of Interleaving Math Practice in Nigeria

Last registered on October 31, 2025
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Pre-Trial

Trial Information

General Information

Title
A Year of Desirable Difficulties: The Impact of Interleaving Math Practice in Nigeria
RCT ID
AEARCTR-0017117
Initial registration date
October 27, 2025

Initial registration date is when the trial was registered.

It corresponds to when the registration was submitted to the Registry to be reviewed for publication.

First published
October 31, 2025, 8:13 AM EDT

First published corresponds to when the trial was first made public on the Registry after being reviewed.

Locations

Country
Nigeria
Region

Primary Investigator

Name
Guthrie Gray-Lobe
Affiliation
University of Chicago
Contact Primary Investigator

Other Primary Investigator(s)

Additional Trial Information

Status
Completed
Start date
2018-09-17
End date
2023-11-01
Keywords
Behavior, Education
Additional Keywords
JEL code(s)
I20, I21, I25, C93
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
Abstract
This 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.
External Link(s)

Registration Citation

Citation
Gray-Lobe, Guthrie. 2025. "A Year of Desirable Difficulties: The Impact of Interleaving Math Practice in Nigeria." AEA RCT Registry. October 31. https://doi.org/10.1257/rct.17117-1.0
Sponsors & Partners
Experimental Details

Interventions

Intervention(s)
This study evaluates the effect of increasing students’ exposure to “desirable difficulties” through interleaved math practice in Nigerian primary schools. Interleaved practice involves alternating between problems requiring different solution methods (e.g., addition, fractions, geometry) rather than practicing a single type of problem repeatedly (“blocked practice”).

The intervention modified the sequence of problems in teacher guides used during daily math lessons in grade 5 classrooms. Schools assigned to the interleaving condition received digital lesson scripts where practice problems alternated across topics, while comparison schools retained the existing blocked format, in which all practice items reinforced the same topic of the day.

The program was implemented by Bridge Nigeria (a subsidiary of NewGlobe) over one full academic year (three terms), affecting all grade 5 students in participating schools.
Intervention (Hidden)
Intervention Start Date
2018-09-17
Intervention End Date
2019-06-26

Primary Outcomes

Primary Outcomes (end points)
Cumulative (end-of-year) assessment
Termly posttests
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
Randomization Unit: School (one Grade 5 classroom per school).

Randomization Method: Stratified by pre-assignment characteristics, including:

- Lesson completion rate (above/below 75%),

- Student–teacher ratio (≤ 15, 15–30, > 30), and

- Urban/rural classification.

Randomization produced 28 schools in the interleaved-practice group and 34 in the blocked-practice group.

Sample: 62 Bridge Nigeria schools (private low-cost schools in Lagos and Osun States).

Final analysis sample includes ~687 students enrolled at baseline.

Treatment Group: Teachers received revised digital lesson guides for Grade 5 math that replaced blocked “my turn / your turn” problem sequences with interleaved ones. The total number, difficulty, and types of problems were identical to the comparison condition, differing only in their sequence.

Comparison Group: Teachers used the standard blocked problem sets used in Bridge schools, where each day’s practice focused exclusively on a single topic.
Experimental Design Details
Randomization Method
Randomization by computer
Randomization Unit
School
Was the treatment clustered?
Yes

Experiment Characteristics

Sample size: planned number of clusters
59 schools
Sample size: planned number of observations
687 students
Sample size (or number of clusters) by treatment arms
Schools: 27 T, 32 C
Students: 313 T, 374
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Supporting Documents and Materials
IRB

Institutional Review Boards (IRBs)

IRB Name
IRB Approval Date
IRB Approval Number
Analysis Plan

Post-Trial

Post Trial Information

Study Withdrawal

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Intervention

Is the intervention completed?
No
Data Collection Complete
Data Publication

Data Publication

Is public data available?
No

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials