EIS utilizes non-English speaking Thai teachers to teach the core subjects. These teachers undergo thorough on-the-job-training. This training will be done while the teachers are having their actual classes. On-the-job-training is effective because the teachers "learn more through experience.” The teachers can also learn how to understand and talk in English through their basic knowledge and by utilizing the indigenous resources that are found in the vicinity. Results have demonstrated that non-English speaking Thai teachers and students simultaneously learn the second language using the basic skills that they garnered during their previous years. The learning method is a ladder type (or "scaffolding") wherein the learners will learn by going in upward motion using previous steps in order to go upward.
On-the-job-training will be done through step-to-step basis. First, the teachers will undergo a workshop seminar, led by a highly experienced trainer. The workshop seminar guides the non-English speaking teachers through the different strategies to be used during the actual classes, through the lesson-planning process, etc. Second, the trainer helps the trainees during pre-lesson preparation, while classes are going on. In the pre-lesson preparation, the trainees are instructed on the appropriate words to be used during the class discussions and on preparation of necessary materials (teaching aids) to be used. Through these processes the non-English speaking teacher is speaking English in front of others. Later she/he can teach the subject alone, using English as the medium of instruction.