Despite its potential in foreign language education, the cross-lingual strategy has been marginalized and stigmatized in many EFL contexts including language education in private language schools of Iran. This study aims to uncover the facilitative role of the cross-lingual strategy in foreign language instruction by theorizing experienced language teachers' practice. To this end, some experienced teachers were selected in line with the sampling procedures of Grounded Theory from famous English language institutes of Tehran, the capital city of Iran. Iterative data collection and analysis revealed that first language use can be differentiated based on learners' level of proficiency.For the beginners, it can be used to present classroom management rules, provide learners with the necessary classroom language and establish rapport. Similarly, at intermediate level L1 can be used to check mastery over the teaching points, give vocabulary equivalents, and explain writing rules. As for advanced learners, it can be used to explain the subtleties of grammar and provide learners with ideas to participate in classroom discussion and text processing.