The use of ELT textbooks in multicultural schools is an under-explored issue despite an increasing number of non-Thais studying in the Thai compulsory education system due to mobility within the ASEAN Community. This paper aims to explore the representations of cultural aspects in the ELT textbooks, which are used in a public primary school where Cambodian, Lao, Myanmar, and Thai learners have created culturally and ethnically diverse landscape. Drawing upon the content analysis, the findings reveal five cultural categories ranked in the following order: products (41%), practices (26%), places (20%), persons (6%), perspectives (6%), and unidentified (1%). These cultural aspects are, however, imbalanced and inappropriate due to the misallocation of cultural representations and learners' lack of recognition of the sociocultural background depicted. Language teachers and school administrators have become instrumental in narrowing down the cultural gap that exists between the textbooks' cultural content and learners' sociocultural backgrounds, experience, and contexts. This study can potentially inform language educators, school administrators, policy makers, and textbook writers who are involved in ELT textbook publication to be more culturally sensitive to Thai and migrant learners' cultural milieu. The right to education of these learners should be recognized, valued, and promoted in multicultural schools that meet the objectives of UNESCO Sustainable Development Goal 4 (SDG 4), namely Quality Education, which includes equitable education and recognition of cultural heterogeneity and multiplicity.