The purpose of this study is to analyze how correctly the English teacher acknowledges and uses the assessment tool for CLT (communicative language teaching) when he or she observes another English teacher’s class. The key words closely related to the assessment tool for CLT in the assessment report samples that English teachers submit for another English teacher’s class are coded in corpus data and investigated by case study on individual procedures in class, such as lesson plan, class implementation and management, and evaluation. It turns out that the English teacher observes and assesses the English class in each step focusing on “learning objective” and “clear lesson plans”, “classroom English” and “learning materials”, “management of activities” and “student’s attention and participation.” However, it is necessary for the English teacher to raise awareness about student’s specific demand for English class, teacher’s knowledge of language, time management, transition to the next phrases, and maintenance of order.