Abstarct: There has been a longstanding debate over the use of mother tongue in English as a foreign language classes and whether it should be avoided or welcomed. During the history theoretical perspectives and empirical findings have supported the facilitative role of first language use in teaching a foreign language. However, in some contexts such as the EFL context of Iran practitioners are unwilling to make use of it and the ones who use it do not feel secure. This clearly emphasizes that language teaching has followed social norms and assumptions rather than dicta and principles of language teaching and learning. In other words, in spite of being potent, the crosslingual strategy has been marginalized and stigmatized in many EFL contexts including language education in private language schools of Iran. By theorizing experienced language teachers’ perspectives, this study intends to discover the facilitative role of the crosslingual strategy in foreign language instruction. 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 depends on three main factors including learner’s level of proficiency, learner’s age and teacher’s tact. First, L1 use can be differentiated baxsed on learners’ level of proficiency. For beginners, it can be used for classroom management and bilingual presentation of classroom language. It can also be applied to clarify the meaning of problematic concrete words, assign homework, present task and exam instruction and form rapport with the learners. Similarly, the occasions where L1 can be used for the intermediate levels are mastery check, giving vocabulary equivalents, providing ideas, explaining writing rules and clarifying some grammatical structures. As for the advanced learners, it can be used to explain subtleties of grammar, provide ideas and present equivalents of abstract words. The analysis also showed the merits of using first language in the classroom. In addition, the study revealed that L1 ought to be avoided during conversations and discussions.