The main aim of this research was, on the one hand, to investigate the alignment of the National Curriculum Document with Halliday’s (2007) three components of ‘language in education’ – namely ‘learning language,’ ‘learning through language,’ and ‘learning about language’ – within the framework of educational linguistics and to assess the manifestation of these components in Iranian school textbooks, on the other hand. This study utilized a qualitative content analysis method with an interpretive-adaptive approach. To this end, after extracting categories related to Halliday’s aforementioned components, all textbooks across the three linguistic domains of Persian, Arabic, and English were analyzed. The findings indicated that the Iranian National Curriculum Document demonstrates a suitable alignment with the ‘learning language’ and ‘learning through language’ components. Furthermore, regarding ‘learning about language,’ the curriculum document includes explicit statements concerning linguistic topics only for Persian and foreign languages (English), but such a statement is missing for Arabic. The analysis of textbooks showed that only English textbooks and elementary-level Persian textbooks simultaneously cover all four language skills. In higher-level Persian textbooks, the primary focus is on reading and writing, while ‘Arabic, the Language of the Quran’ textbooks predominantly emphasize reading. Additionally, across all educational levels, the language of instruction in all textbooks, with the exception of English textbooks, ‘Quranic Education,’ and ‘Arabic, the Language of the Quran,’ is Persian. In terms of the ‘learning about language’ component, textbooks for all three languages – Arabic, Persian, and English – include linguistic discussions. Moreover, the findings demonstrated a more complete alignment between English and Persian textbooks and the National Curriculum Document, whereas ‘Arabic, the Language of the Quran’ textbooks lack full alignment due to insufficient attention to all language skills and linguistic content within the curriculum document.