Educational systems around the world have long strived for increasing educational equity. Yet, a large body of research has established a prevailing and substantial relation between Socio-Economic Status (SES) and student achievement (OECD, 2016; Sirin, 2005), and this relation seems to increase in the Nordic countries over time (Hansen, 2015; Authors 2016, 2018a, 2018b; OECD, 2016). However, little attention has been devoted to investigating the possible mechanisms through which SES is related to educational achievement. Rather, SES is utilized to control for selection bias when investigating effects of predictors on educational outcomes. Moreover, if the aim is to reduce the strength of the relationship between SES and student outcome, there is a need to identify factors that moderate this relation.

While many studies have found teachers and their instruction to be key to student outcomes, only few have linked these to equity, and even fewer in the Nordic countries (Darling-Hammond, 2015; Hwang, Choi, Bae, & Shin, 2018). However, some studies from Germany and the USA found that high-quality teachers may enhance equity by reducing the gap between high- and low-SES students (Baumert et al., 2010; Darling-Hammond, 2015; Rjosk et al., 2014). While high-SES students may be supported by their parents in their school work, high-quality teachers may compensate for low-SES students’ lack of such support (Jeynes, 2005). By improving teacher quality, their competence, and instruction, more students may reach their potential (Rivers & Sanders, 2002; Rjosk et al., 2014).

Formal qualifications, including educational level, specialization, and professional development have been linked to high-quality teachers (Blömeke, Suhl, Kaiser, & Döhrmann, 2012). While there are mixed results with regards to the effects of teachers’ educational level, several studies have found effects of their specialization on student outcomes and equity (e.g., Goe, 2007). In the USA, some researchers suggest increasing professional development for teachers to help close the gap between students (Darling-Hammond, 2015). Indeed, meta-analyses and reviews suggest that teacher professional development may have significant effects on student achievement (effect sizes > .50) (Goe, 2007; Timperley, Wilson, Barrar, & Fung, 2007).

Starting in 2013, a massive teacher professional development program in mathematics was implemented in Sweden and it has been extended to other subjects (Ringarp & Parding, 2018). In Norway too, investments have been made in teacher professional development and improving teacher quality (Regjeringen, 2014), albeit less massively than in Sweden. Given the decreasing levels of equity and the increasing emphasis on teacher quality and professional developement in these Nordic countries, the question arises whether teacher quality may reduce the relation between SES and achievement.

However, teacher quality is rarely directly related to student outcomes; instead, there is an indirect effect via instructional quality (e.g., Baumert et al., 2010). Hence, researchers that examine whether teacher quality may moderate the relation between SES and achievement, should also consider indirect effects via instructional quality, that is, a possible mediational path.

The overall purpose of this study is two-fold: (1) to identify the aspects of teacher quality and their instruction that may reduce the relation between SES and student achievement in Norway and Sweden (moderation), and (2) to examine whether the moderation effect of teacher quality is (partially) mediated via instructional quality (mediated moderation).

Data We utilized the large-scale data from Trends in Mathematics and Science Study (TIMSS), the only study with representative samples at the national level that collect data from students and teachers in mathematics and science. Seeing how teacher quality seems to be of more importance for student outcomes in lower secondary than in primary school (Goe, 2007; Authors, 2018), we selected grade-8 students from the only two Nordic countries participating in the last cycle of TIMSS in 2015: Norway and Sweden. Measures Instructional quality was measured using teachers’ ratings of how often they would do certain practices (measured by a four-point scale from never to every, or almost every, lesson). In accordance with theory (e.g., Klieme, Pauli, & Reusser, 2009), we included 5 items pertaining to cognitive activation (e.g., “Ask students to complete challenging exercises that require them to go beyond the instruction”), teacher support (e.g., “Encourage classroom discussions among students”), and clarity of instruction (e.g., “Link new content to students’ prior knowledge”). Teacher quality was measured through indicators of qualifications, including Educational level (from ISCED level 3 to 8), Specialization (major or main area of study in science education and/or in physics, biology, chemistry or earth science), and Professional development (number of hours spent in professional development in the last two years), and the Content of Professional development (Science content, Science pedagogy/instruction, Science curriculum, Integrating information technology into science, Improving students’ critical thinking or inquiry skills, and Science assessment). SES was measured by students’ report on parents’ education, number of books at home, and home educational resources, and was represented as a latent variable rather than a composite score. Science achievement was measured using the first plausible value (all five plausible values will be included in the final model). Data Analysis First, measurement invariance between Norway and Sweden for all constructs was investigated. Next, multi-group, multilevel structural equation models with random slopes were employed (students nested in classes). Cross-level interaction models with mediational paths were built to test which aspects of teacher quality moderate the relation between SES and student mathematics achievement via instructional quality. All models were estimated in Mplus 8 using the robust maximum likelihood estimation. Prior to adding any structural models, confirmatory factor analyses were conducted to ensure reliable and valid measurement models. Mediation effects were estimated via the MODEL CONSTRAINTS option in Mplus.

Preliminary findings showed metric invariance for all constructs at the classroom level. It was therefore possible to compare relations between these and other variables across Norway and Sweden. The relation between SES and achievement was higher in Sweden than in Norway at the classroom level. For teachers’ educational level, there were no significant moderation effects in either of the countries. For professional development, there was a significant and negative moderation effect of the relation between SES and achievement via instructional quality in Sweden, but not in Norway. Professional development consequently reduced the strength of the relation between SES and achievement, thus enhancing equity in Sweden. The same was the case for teachers’ specialization, although the moderation effect was weaker (but significant). Regarding mediated moderation, there was only a significant mediation of the moderation effect of professional development via instructional quality in Sweden. Seeing how Sweden has invested tremendous effort and resources into professional development, the findings are in line with those from the USA (e.g., Darling-Hammond, 2015), and indicate that such efforts may reduce the performance gap between high- and low-SES students. The reason why there were no significant findings for Norway could be related to the scale and content of the professional development implemented. Effective programs tend to be of considerable length, focus on content, active learning, and collaborative activities, and involve collegial collaboration on cases, discussions, reflection, and continuous feedback (e.g., Timperley et al., 2007). This study contributes to teacher education, educational effectiveness, and especially educational policy, as it demonstrates that teachers may make a difference in reducing inequity through their competence and instruction.

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