This doctoral thesis aims to explore Sweden’s achievement gap in international assessment and how this may have developed in the context of a network of educational inequalities. Theoretically grounded in the Model of Potential Educational Experiences (Schmidt, Raizen, Britton, Bianchi, & Wolfe, 1997), the thesis investigates how the relationship between the intended and attained curriculum is moderated by actions at the classroom level. Teacher implementation of the curriculum provides opportunities for students to learn yet is a source of inequity in the school system. Student socioeconomic background and the amount of subject content (or Opportunity to Learn – OTL) they are exposed to are judged to significantly influence student outcomes. Socioeconomic inequality of outcomes has been perennially observed in educational assessment and has been a topic of investigation since the mid-twentieth century, while a body of literature suggests that there is an equality gap in OTL, with more advantaged students offered more content coverage through their mathematics lessons. This compilation thesis features an integrative essay and three empirical studies, which apply statistical analysis to data from two international large-scale assessments, PISA and TIMSS. Study I investigated the measurement of socioeconomic status over time in Sweden. After establishing which questionnaire items consistently appeared in PISA, a measurement model bespoke to Sweden was constructed from 2000 data. The model was found to be replicable and trustworthy over time, establishing an alternative measure of SES applicable to 15 years of Swedish PISA data. In Study II socioeconomic inequalities in opportunity and outcomes in mathematics and science, and the question as to whether unequal opportunities perpetuate unequal outcomes were investigated in 78 countries using 4 cycles of TIMSS data. Achievement gaps were observed near universally. These achievement gaps were strong and increased across the cycles of TIMSS. Opportunity gaps were less frequently observed, and evidence that schooling exacerbates socioeconomic inequalities in outcomes was confined to a select group of countries including England, Malta, Scotland, and Singapore. Sweden’s achievement gap was consistent across the time points, and an opportunity gap was only observed in half the cycles. Finally, schooling mediated the effects of SES on achievement in only the 2003 cycle for Sweden, suggesting equitable mathematics provision in Sweden. Teachers are essential to the implementation of the curriculum, and their actions affect the experiences of students. Multiple inequalities in Swedish classrooms were explored in Study III. The 2015 TIMSS cycle was grouped by whether or not teachers were mathematics specialists. Overall, Swedish mathematics students experienced substantial gaps in achievement, opportunity and teacher quality. However, differing patterns of inequalities emerged in the grouped model. Among classes with specialist teachers there was a moderate opportunity gap, while those with non-specialists had a teacher quality gap. In both groups there was a socioeconomic gap in teacher perception of school ethos towards academics. The findings of this study underscore the importance of having high-quality teachers in mathematics classrooms as a temper of outcome inequity. Collectively, the findings of the constituent studies confirm the persistence of the achievement gap in Sweden and globally, contextualize the opportunity gap in Sweden, and underline the importance of item choice and construct measurement when modelling inequality using international data. Suggestions are made for further research integrating the thesis’s contribution to construction measurement into trend analyses of opportunity gaps, and combining register and international data to parse how changes in teacher education may affect equality in Swedish classrooms. Parts of work I. Rolfe, V. (2021). Tailoring a measurement model of socioeconomic status: Applying the alignment optimization method to 15 years of PISA, International Journal of Educational Research, 106. visa artikel II. Rolfe, V., Strietholt, R., & Yang Hansen, K. (under revision). Does inequality in opportunity intensify inequality in outcomes? International evidence from four TIMSS cycles. III. Rolfe, V., Yang Hansen, K., & Strietholt, R. (under revision). Integrating educational quality and educational equity into a model of mathematics performance.