The research aims to enhance the handling of modal verbs (MVs) in EFL textbooks by leveraging perspectives from corpora that include both native speakers' language data and the language data of individuals who are learning the language. To assess the authenticity of language in textbooks, an analysis between the native corpus and a collection of language data compiled from textbook is conducted. The research delves into the developmental patterns of MV usage among learners through a stratified analysis of student essays (Grades 7, 8, 9). Comparisons between learner patterns and a graded textbook series are made to ascertain potential correlations. A novel aspect of the examination explores how the salience and complexity of L2 forms and functions shape the impact of EFL textbooks on learner production. Findings reveal significant differences in the use of MVs between EFL textbooks and the British National Corpus (BNC). Moreover, analysis of student essays indicates a substantial influence of textbooks on learners' MV usage. The study proposes strategies to enhance EFL textbook design, advocating for authenticity and learner-centric approaches. Utilizing native and learner corpora facilitates targeted instruction, addressing common errors and challenges. The incorporation of authentic language examples from the native corpus is recommended to expose learners to real-world language use. This research underscores the significance of integrating native and learner corpora insights in EFL textbook design, ultimately fostering more effective language learning outcomes.