This study examines how subject-based instruction contributes to language development and tolerance formation in a multicultural upper secondary classroom within a trilingual educational context. The study addresses the following research questions: How does sustained subject teaching support students’ adaptation to Kazakh-medium instruction? In what ways do subject lessons contribute to the development of tolerance and intercultural understanding in a multilingual classroom?

The research is grounded in theoretical perspectives on content-based language learning and sociocultural theory. Content-based and subject-based language learning frameworks emphasise the integration of language development with disciplinary knowledge, suggesting that academic language emerges most effectively through meaningful engagement with subject content. From a sociocultural perspective, learning is understood as a socially mediated process in which interaction, collaboration, and guided participation play central roles in cognitive and linguistic development.

The study is further informed by theories of intercultural education and value-oriented pedagogy, which highlight the role of schooling in fostering mutual respect, civic responsibility, and inclusive social relations in culturally diverse contexts. Within this framework, tolerance is conceptualised not as a passive attitude but as an outcome of sustained pedagogical practice, reflective dialogue, and structured interaction among learners.

Empirically, the study draws on a longitudinal case study conducted at a Nazarbayev Intellectual School in Kazakhstan. The focal group consists of a Grade 11 class of 23 students from diverse ethnic backgrounds, including Kazakh, Russian, Uyghur, Uzbek, Korean, and Chinese learners. A substantial proportion of the students had not previously studied academic subjects in Kazakh, which initially created linguistic and academic challenges in history, geography, and language lessons.

The European and international relevance of the study lies in its contribution to current debates on multilingual and multicultural education. Across European educational systems, schools increasingly face the challenge of integrating linguistically and culturally diverse learners into mainstream subject instruction. The study offers insights into how subject-based teaching can function as a bridge between language learning and value education, supporting both academic achievement and social cohesion.

By linking teachers’ instructional decisions to students’ evolving linguistic and social outcomes, the study aligns closely with the ECER 2026 theme “Knowing and Acting” and contributes to international discussions on teacher agency, inclusive education, and the transformative potential of subject teaching in multilingual learning environments.

This study adopted a qualitative, practice-based longitudinal case study design. The research was conducted at a Nazarbayev Intellectual School of Natural Science and Mathematics in Almaty, Kazakhstan, over a period of three to four years from Grade 7 to Grade 11. The participants were 23 students from a Grade 11 multicultural class representing diverse ethnic backgrounds, including Kazakh, Russian, Uyghur, Uzbek, Korean, and Chinese learners. In addition, 14 parents participated in semi-structured interviews. Ethical principles of confidentiality and voluntary participation were strictly observed. Data were collected using multiple sources to ensure triangulation. First, a five-item student questionnaire was administered to identify language-related difficulties and learning experiences. Second, semi-structured interviews were conducted with parents from non-Kazakh ethnic backgrounds to explore perceptions of multilingual instruction and adaptation processes. Third, systematic classroom observations were carried out in history, geography, Kazakh language, and English lessons, with attention to interaction patterns, peer support, and language use. In addition, students’ written assignments, posters, and project work were analysed as supplementary data. Data were analysed using qualitative content analysis. Analytical categories included language adaptation, subject-based language development, peer collaboration, parental involvement, and tolerance formation. Developmental changes across different stages of schooling were compared to identify academic and social trends over time.

The findings indicate that sustained subject-based instruction played a central role in students’ language development and social adaptation in a multicultural classroom. Over time, the integration of linguistic support within history, geography, and language lessons contributed to improved academic language proficiency and increased confidence in classroom participation. History education emerged as a key space for integrating language development with value formation. Through collaborative tasks, reflective discussion, and project-based learning, students developed not only disciplinary knowledge but also mutual respect and intercultural understanding. These practices supported the gradual formation of tolerant peer relationships and inclusive classroom interaction patterns. Parental involvement further strengthened students’ adaptation to Kazakh-medium instruction. As students demonstrated academic progress and increasing independence, parental attitudes became more supportive of multilingual education and school practices. The study suggests that tolerance is not an automatic outcome of diversity but the result of deliberate pedagogical design and sustained value-oriented practice. Subject-based instruction, when aligned with institutional values and collaborative learning strategies, can promote both academic achievement and social cohesion in multicultural educational settings.

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