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The Use of Homework to Introduce Spaced Practice

Mitigating the Achievement Gap Between End-of-Topic and Exam Assessments in Secondary Science

Author: A. Fortini

Research project completed as part of the Postgraduate module in education research, University of Sheffield Hallam, 2019.

(This webpage was generated with the help of AI, using the original research report as a source.)

Action Research Report Key Stage 3 Science Cognitive Science & Pedagogy Spaced & Interleaved Retrieval

Abstract

In many secondary schools, topics are taught and tested in blocks, with each topic dealt with separately. This can produce good results on immediate end-of-topic (EOT) tests, but students may forget much of the material before the end-of-year (EOY) examination. In the historical baseline data for this project, the gap was between -5% and -22%. This research project looks at whether weekly homework quizzes using spaced and interleaved retrieval can reduce this gap without taking up additional lesson time. A Year 9 cohort was studied across consecutive Chemistry (blocked practice) and Biology (spaced practice) blocks. The change in retention was measured using summative assessments.

The results show a clear reduction in knowledge loss: the average performance drop fell from -8.1 ± 3.2 marks with massed practice to -1.2 ± 2.0 marks with spaced practice. This is a difference of +6.9 marks in favour of the spaced approach (p < 0.05, Cohen's d = 2.586). There was, however, a practical cost. Weekly homework non-completion almost doubled, from 3.2 to 6.3 pupils per week. Overall, the results suggest that using homework for spacing can help students retain knowledge for longer, but it needs to be supported by a consistent approach to homework completion.

1.0 Practice Issues

Knowledge retrieval plays a pivotal role in student attainment during examinations. While pure recall accounts for only 20% of marks in a typical GCSE paper, answering higher-order analysis and application questions is impossible without fast, reliable access to core information.

It has been over a century since Hermann Ebbinghaus first mapped the forgetting curve, and subsequent research has consistently shown that spacing out recall practice dramatically increases long-term retention (van Weringh et al., 2015). Despite this robust body of evidence favoring spaced and interleaved learning, "blocking" remains the predominant delivery structure in school schemes of work (Rohrer, 2012).

In a typical scheme of work, pupils encounter topics in blocked sequences structured like this:

Blocked Learning Sequence:
[A A A] → (End-of-Topic Test A) → [B B B] → (End-of-Topic Test B) → [C C C] → (End-of-Topic Test C) → [D D D] (End-of-Year Exam)

Assessments occur immediately after each topic unit, followed by a cumulative end-of-year examination assessing all material simultaneously. Consequently, as Weimer (2014) notes:

"typically the first time that our students see the content out of order is on the exam."

The Achievement Gap

An analysis of Year 8 achievement data for the intervention group highlights the practical impact of this blocked model (see Figure 1; selection criteria for the intervention group are detailed in Section 2).

Figure 1 illustrates the percentage difference between end-of-year exam scores and average end-of-topic test scores for the 2017/18 academic year. Every pupil in the cohort performed worse on the end-of-year examination than on their individual topic tests, with performance drops ranging from -5% to -22%.

This pronounced dip in performance stems from two main factors:

  1. Inefficient study habits: Pupils may rely on revision methods that are not very effective before important assessments.
  2. Forgetting over time: Pupils may find it difficult to remember topics that were taught several months earlier without regular retrieval practice.

Both issues could originate from the absence of distributed practice—specifically spaced and interleaved learning—within the core curriculum scheme of work.

2.0 Project Plan and Rationale

The project addresses a primary and a secondary research question:

Main Research Question: How does the spacing of topics in weekly homework quizzes impact the attainment of Year 9 students at the end of year assessments, compared to the end of topic tests?

Secondary Research Question: Given the desirable difficulties introduced by my chosen distributed practice, does spaced and interleaved homework affect the percentage of students that complete it?

2.1 Intended Outcomes and Impact

Outcomes for Teachers

Outcomes for Pupils

2.2 Why the Intervention Was Chosen

The educational research literature offers an overwhelming consensus regarding the efficacy of spaced and interleaved learning practices in improving long-term knowledge retention. The Education Endowment Foundation (EEF, 2014) also underscores that structured spacing strategies yield substantial gains in student progress.

However, implementing spacing in live classrooms often meets resistance due to explicit time constraints within schemes of work (SOW) or a general lack of adaptive resources. To completely circumvent these problem, this intervention uses homework as the primary tool for spacing and interleaving.

The intervention relies on the idea of "desirable difficulties" (Bjork, 1994; Weimer, 2017). Spacing forces a degree of forgetting, requiring pupils to work harder to recall facts encountered weeks earliers. Furthermore, by blending spacing with interleaving (Rohrer, 2012), students are pushed to actively discriminate between scientific concepts.

2.3 Methodology and Design

The Year 9 Science scheme of work is strictly divided into the three sciences: Chemistry, Biology, and Physics, delivered sequentially. To eliminate researcher bias, the practitioner's primary subject specialization—Physics—was entirely excluded from the experimental design.

During the initial Chemistry block, students followed the standard SOW, and the weekly homework was strictly blocked. The performance drop between the short-term end-of-topic tests and the delayed end-of-subject tests establishes a local baseline for our standard "achievement gap". In the Biology block, the intervention is introduced via the weekly homework structure, preserving traditional lesson instruction perfectly.

3.0 Presentation of Results

The collected data shows distinct shifts between the Chemistry progress (standard blocked practice) and the Biology progress (spaced and interleaved practice).

Chemistry Progress

(No Intervention Baseline)

-8.1 ± 3.2

Marks Deviation

Biology Progress

(With Spacing Intervention)

-1.2 ± 2.0

Marks Deviation

Post HW Non-Comp

(Difference)

6.3 ± 1.1

Marks difference

The Chemistry baseline results empirically confirm the existence of a substantial achievement gap between short-term end-of-topic (EOT) tests and delayed end-of-year (EOY) tests. Student retention experienced a notable decay (-8.1 marks). On the other hand, the introduction of spacing and interleaving within the Biology unit resulted in a drastic reduction of this gap, with an average deviation of just -1.2 marks.

3.1 Data Visualizations

The chart below displays the comparative retention performance metrics, demonstrating the improved student grades under spacing intervention compared to the blocked practice.

Comparative Curricular Progress (Mean Mark Shifts)

-8.1
Chemistry Progress (Control)
-1.2
Biology Progress (Intervention)

3.2 Statistical Calculations

Pooled Standard Deviation (SDpooled): 2.668

Calculated Progress Difference Gain: +6.90 Marks in favor of spacing intervention.

Cohen's d Effect Size: 2.586 (Exceptional Academic Growth Shift)

Calculated Student t-value: 5.172

Statistical Evaluation: The calculated t-value (5.172) vastly exceeds the critical table threshold value of 2.145 for an alpha level of p < 0.05 at 14 degrees of freedom (df). The difference in retention profiles is highly statistically significant.

3.3 Data Validity and Cohort Consistency Considerations

4.0 Discussion

The quantitative findings of this research project provide strong support for the integration of distributed and interleaved practice into the weekly homework structure of secondary science. The primary question aimed to determine whether spacing topics in weekly homework quizzes could mitigate the traditional achievement gap between immediate testing and delayed summative assessments. The baseline data from the Chemistry control phase clearly illustrated this decay, with an average reduction of -8.1 ± 3.2 marks.

The introduction of the 8-week spacing and interleaving framework in the Biology block successfully changed this trend, limiting the performance drop to a negligible -1.2 ± 2.0 marks. A comparison of these two shifts reveals an absolute attainment benefit of +6.9 marks for the intervention group. This difference is highly statistically significant, as shown by the calculated t-statistic of 5.172, which easily exceeds the critical threshold of 2.145 (α = 0.05, df = 14). Furthermore, the calculated Cohen's d effect size of 2.586 represents a substantial improvement in educational attainment, well above the standard criteria used by the Education Endowment Foundation to identify highgly effective interventions.

These findings align closely with the cognitive frameworks established by Bjork (1994) and Rohrer (2012). By breaking up the homework assignments, the intervention forced a structured period of forgetting, requiring students to engage in higher cognitive effort to reconstruct and retrieve historical concepts (B1, B2, B3) while simultaneously learning new information. This process directly leverages the mechanics of desirable difficulties (Bjork, 1994). Additionally, the interleaved design prevented students from mindlessly applying the same solution strategy to an entire block of uniform questions (Rohrer, 2012). Forcing students to continuously distinguish between changing biological topics built stronger conceptual discrimination, ensuring their understanding remained secure for the comprehensive end-of-subject exam.

However, the secondary inquiry revealed an important trade-off . The introduction of these cognitive challenges led to a significant increase in weekly homework non-completion rates, which nearly doubled from a baseline of 3.2 ± 0.9 pupils to 6.3 ± 1.1 pupils. This trend confirms that students find spaced and interleaved homework formats more difficult and less intuitive than standard massed homework formats.

References