Ahmad Hadadi - Department of Foreign Languages, Arak University, Markazi, Iran
Ahmad Goodarzi - Department of Foreign Languages, Arak University, Markazi, Iran
Hamed Abbasi - Department of Foreign Languages, Arak University, Markazi, Iran

Several second language acquisition specialists such as Jarvise (2000), Corder (1978), Taylor (1975), Kellerman (1983), and Jewitt (2006) have proposed different views toward L1 transfer during L2acquisition. A number of studies show that the influence of the L1 is developmentally constrained in the sense that it only occurs when the learner has reached a stage of development that provides a crucial similarity measure. In other words, studies have produced very mixed results. The main question to be answered in this study is how L1 influence changes with regard to L2 proficiency increase. The research is being carried out in the form of 7 in-depth longitudinal case studies with EFL teachers at different levels of teaching experience. The aim is to provide a unique Web-based resource to support further research and professional pedagogical development into how learning inclassrooms has been impacted by L1 influence with regard to L2 proficiency increase. Research data are being collected via a variety of ethnographic research instruments, namely classroom observations and field notes, video recordings of school lessons, and in-depth interviews and video-triggeredreflective dialogues with the teachers and students and teacher’ action research in L1 influences in schools of Iran. Findings suggest that, although L1 can provide a leg-up along the developmental ladder, L1 influence cannot increase or decrease with regard to L2 proficiency, rather its influence remain stable. The research is significant in suggesting that, this is the crucial similarity measures which determine the stability of L1 influence.