Purpose: English as Foreign Language (EFL) teachers tend to demonstrate low literacy levels in instructional materials and feel unprepared to use materials effectively. To better prepare pre-service EFL teachers for real classrooms that they will teach upon graduation, current K-12 teachers can provide significant insights into the needed competences of prospective teachers. With this purpose, the study aimed to investigate the competences in utilizing instructional materials needed by EFL teachers to become effective teachers to teach at the context of K-12 public schools. Research Method: The study used qualitative research methods. Data were collected through semi-structured interviews from 19 veteran EFL teachers teaching at K-12 public schools in Ankara. In order to gain a wide range of teacher perspectives on the knowledge and skill requirements for instructional materials, a maximum variation sampling technique was used. Data were subjected to content analysis. Findings: The results suggested that pre-service EFL teachers need to be competent in using a wide range of instructional materials (i.e., printed, visual, authentic, technological, web-based and self-produced) and material related areas (i.e., adaptation, selection, use and design) to use materials for different purposes (i.e., motivational, instructional, classroom management, for general or overall improvement of students and learnability) under some challenging conditions that may affect their utilization of instructional materials. Implications for Research and Practice: In case that the expected competences are adequately addressed at teacher-education programs, the disconnection between the universities and school environment could be solved and pre-service EFL teachers would feel ready and competent to teach upon graduation from teacher education programs.