The current mixed-method study probed EFL instructors' mediative knowledge across four different contexts of teaching including language institutes, universities, and senior and junior high schools in Iran. To this end, 181 EFL instructors, 80 males and 101 females, completed mediative closed-questionnaire which composed of twelve items to measure EFL instructors' knowledge of mediation across context. Out of 181, 72 participants, 16 (22%) institute instructors, 20 (28%) university instructors, 19 (26.38%) senior instructors, and 17 (23.61%) junior instructors participated in oral interview. Results of descriptive statistics and Chi-square showed that there exist significant differences among EFL instructors in seven mediative items; furthermore, the difference shows that there exists relationship between EFL instructors' mediative knowledge across the contexts; however, in five mediative items, no differences were found across contexts. Results of oral interview of EFL instructors in terms of assessment revealed that they mostly believed that learners through instructors' guidance should self-assess their learning and behavior. To achieve such an end, they suggested instructors' step by step scaffolding and strategic deliverance of assessment to the learners. In terms of cooperation and individualization, the results of oral interview revealed that instructors believed in unified improvement of both of them. To improve both, pair and group works were suggested to boost cooperation whereas competition and individual activities were suggested to foster individualization. Context variation due to its own community and unique characteristics, learners' potential to self-assess their learning, and development of whole learner were suggested to be taken into consideration by instructors, educationalists, parents, and curriculum, and course designers.