In the TIMSS 2023 cycle, Swedish Grade 8 students showed a significant improvement in mathematics achievement compared to 2019. While their performance has not yet returned to the high levels seen in 1995, students now score higher on average than in 2003. Specifically, Swedish students improved their TIMSS results by an average of 14 points, outperforming the EU and OECD averages and ranking above other Scandinavian countries (Swedish National Agency for Education, 2024). This progress stands out within Sweden’s highly decentralized educational system, which emphasizes competition among schools. Such a system, as described by Böhlmark and Lindahl (2015), often amplifies disparities in educational resources and outcomes, making the observed improvement particularly noteworthy.

Swedish education has faced longstanding challenges, including increased socioeconomic segregation following the educational reforms of the 1990s (Yang Hansen & Gustafsson, 2019). Understanding the factors contributing to these recent gains in achievement is crucial, especially in identifying whether the positive trend is attributed by the improvement of all students. 

As a multidimensional construct, instructional quality includes practices that create the necessary conditions for student success and learning (Charalambous et al., 2021). Unlike formal teacher qualifications, instructional quality reflects observable classroom behaviors and interactions (Nilsen et al., 2016). Research has repeatedly shown that instructional quality is a key determinant of performance across subjects (Atlay et al., 2019), and high-quality instruction is essential for improving student outcomes (Fauth et al., 2019). Moreover, instructional quality has been shown to be linked with reduced educational inequities (Berkowitz, Moore, Astor & Benbenishty, 2017).

Given these findings on instructional quality, and the observed improvement in mathematics performance between TIMSS cycles of 2019 and 2023, this study aims to investigate whether changes in instructional quality have contributed to this positive trend. Specifically, we examine whether improvements in instructional quality, specifically classroom management and instructional clarity, mediated changes in mathematics achievement over time.

This study adopts the Three Basic Dimensions (TBD) framework (Praetorius et al., 2018) to conceptualize instructional quality. Originally developed in Germany for assessing mathematics instruction, the TBD framework is widely applicable across subjects, grades, and educational systems, making it particularly suitable for the Swedish context. The framework, validated in numerous national and international studies, focuses on core dimensions of instrsuctional quality, of which this study addresses two: classroom management and instructional clarity. We hypothesize that improvements on management of classroom and teacher’s ability to deliver content in a clear, structured, and understandable way may relate with the improvements in achievement in TIMSS 2019 and 2023.

The research questions guiding this study are:

1. Have there been changes in the levels of instructional quality and SES from 2019 to 2023?
2. What is the impact of these changes on the changes in mathematics achievement of Swedish eighth graders between 2019 and 2023?

This study utilizes TIMSS 2019 and 2023 data, comprising 3,965 students in 2019 and 5,046 in 2023. Classroom management and instructional clarity indicators were derived from student responses on a 4-point Likert scale. For classroom management, sample items include “There is disruptive noise” and “My teacher has to wait a long time for students to quiet down.” For instructional clarity, examples include “My teacher is good at explaining mathematics” and “My teacher explains a topic again when we don’t understand.” Socioeconomic background was controlled using the Home Educational Resources scale (HER). Mathematics achievement was measured using the five plausible values provided by the IEA, analyzed through multiple imputation techniques. All constructs were tested for measurement invariance to ensure comparability across the two TIMSS cycles. Understanding the reasons behind changes in achievement is challenging due to the complexity of educational processes and the cross-sectional design of most International Large-Scale Assessments (ILSAs). Cross-sectional studies capture data at a single point in time, making it difficult to distinguish causes from effects, as causation requires that causes precede effects. Although causal inferences are limited due to the absence of repeated measures for the same individuals, sophisticated methodologies can leverage TIMSS’s trend data to produce robust insights (Gustafsson & Nilsen, 2022; Nilsen & Gustafsson, 2014; Rosén & Nilsen, 2024). To investigate whether changes in instructional quality and SES explain the observed improvement in mathematics performance, a mediation structural equation model (SEM) grounded in a Difference-in-Differences (DiD) approach was applied. Data from TIMSS 2019 and 2023 were merged using the IDB Analyzer, with a "Time" variable distinguishing the two cycles (coded as 0 = 2019 and 1 = 2023). Analyses in Mplus 8 (Muthén & Muthén, 1998–2017) used the “TYPE=COMPLEX” option to account for the hierarchical structure of the data, using IDCLASS as the cluster variable. House weights and the robust maximum likelihood estimator (MLR) were applied. Null models first examined changes in mathematics achievement, SES, classroom management, and instructional clarity, using TIMSS cycle as the independent variable. These models served as simple mean comparisons. Subsequently, a mediation model was developed to test whether SES or instructional quality mediated the effect of time on mathematics achievement. In this model, indirect effects capture the estimated impact of SES or instructional quality on the observed improvement in mathematics achievement over time. Model fit was assessed using local and global fit indices to ensure reliability and validity.

Preliminary analyses yielded well-fitting measurement models for the latent constructs of instructional clarity and classroom management, with measurement invariance confirmed across TIMSS 2019 and 2023. The results indicate that both constructs improved over this period and significantly mediated the observed increase in student mathematics achievement. Additionally, SES remained a strong predictor of achievement, with results suggesting that the overall improvement was not driven by significant changes in SES distribution. While the study does not establish causal relationships, the findings suggest that enhanced classroom management and instructional clarity shifts may partially explain the positive trend in mathematics achievement. This study contributes to the field by offering evidence that improvements in these classroom practices, are associated with better student outcomes. Additionally, the methodological approach employed, provides a framework for investigating the relationship between contextual factors and achievement trends. Understanding the dynamics behind changes in educational achievement is a critical goal for policymakers, practitioners, and researchers alike. This study highlights the potential of leveraging ILSA data to explore how improvements in key classroom practices can contribute to national educational progress. Researchers and practitioners may find this approach valuable for examining similar questions in other contexts, as it produces robust, reliable, and valid results, and may support their efforts to improve educational equity and effectiveness.

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